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Journal Articles

Simultaneous sequestration of Co$$^{2+}$$ and Mn$$^{2+}$$ by fungal manganese oxide through asbolane formation

Aoshima, Miku*; Tani, Yukinori*; Fujita, Rina*; Tanaka, Kazuya; Miyata, Naoyuki*; Umezawa, Kazuhiro*

Minerals (Internet), 12(3), p.358_1 - 358_16, 2022/03

 Times Cited Count:4 Percentile:82(Geochemistry & Geophysics)

In this study, we conducted sequestration experiments of Co$$^{2+}$$ by ${it Acremonium strictum}$ KR21-2 in a Mn$$^{2+}$$/Co$$^{2+}$$ binary solution at pH7. The sequestration of Co$$^{2+}$$ by newly formed BMOs readily progressed in parallel with the exogenous Mn$$^{2+}$$, with higher efficiency than that in single Co$$^{2+}$$ solutions. This is attributed to a synergetic effect on Co$$^{2+}$$ sequestration through the formation of asbolane in Mn$$^{2+}$$/Co$$^{2+}$$ binary systems.

Journal Articles

R&D plan for development of oxidation-resistant graphite and investigation of oxidation behavior of SiC coated fuel particle to enhance safety of HTGR

Ueta, Shohei; Sumita, Junya; Shibata, Taiju; Aihara, Jun; Fujita, Ichiro*; Ohashi, Jun*; Nagaishi, Yoshihide*; Muto, Takenori*; Sawa, Kazuhiro; Sakaba, Nariaki

Nuclear Engineering and Design, 271, p.309 - 313, 2014/05

 Times Cited Count:9 Percentile:57.68(Nuclear Science & Technology)

A new concept of the high temperature gas-cooled reactor (HTGR) is proposed as a challenge to assure no event sequences to the harmful release of radioactive materials even when the design extension conditions (DECs) occur by deterministic approach based on the inherent safety features of the HTGR. The air/water ingress accident, one of the DECs for the HTGR, is prevented by additional measures (e.g. facility for suppression to air ingress). With regard to the core design, it is important to prevent recriticality accidents by keeping the geometry of the fuel rod which consists of the graphite sleeve, fuel compact and SiC-TRISO (TRIstructural-ISOtropic) coated fuel particle, and by improving the oxidation resistance of the graphite when air/water ingress accidents occur. Therefore, it is planned to develop the oxidation-resistant graphite, which is coated with gradient SiC layer. It is also planned that the experimental identification of the condition to form the stable oxide layer (SiO$$_{2}$$) for SiC layer on the oxidation-resistant graphite and on the SiC-TRISO fuel. This paper describes the R&D plan for un-irradiation and irradiation test under simulating air/water ingress accident condition to develop oxidation-resistant graphite and to investigate the oxidation behavior of SiC coated fuel particle.

Journal Articles

Development of evaluation method with X-ray tomography for material property of IG-430 graphite for VHTR/HTGR

Sumita, Junya; Shibata, Taiju; Fujita, Ichiro*; Kunimoto, Eiji*; Yamaji, Masatoshi*; Eto, Motokuni*; Konishi, Takashi*; Sawa, Kazuhiro

Nuclear Engineering and Design, 271, p.314 - 317, 2014/05

 Times Cited Count:11 Percentile:65.01(Nuclear Science & Technology)

In this study, in order to develop evaluation method for material properties and to evaluate the irradiation-induced property changes under higher neutron doses for IG-430, the oxidation and densification effects on elastic modulus of IG-430 were investigated. Moreover, the correlation of the microstructure based on the X-ray tomography images and the material properties was discussed. It was shown that the elastic modulus of the densified graphite depends on only the closed pores and it is possible to evaluate the material properties of graphite by using X-ray tomography method. However, it is necessary to take into account of the change in the number and shape of closed pores in the grain to simulate the elastic modulus of the highly oxidized and irradiated materials by the homogenization analysis.

Journal Articles

Evaluation of fracture toughness of fine-grained isotropic graphites for HTGR

Yamada, Teruaki*; Matsushima, Yuki*; Kuroda, Masatoshi*; Sumita, Junya; Shibata, Taiju; Fujita, Ichiro*; Sawa, Kazuhiro

Nuclear Engineering and Design, 271, p.323 - 326, 2014/05

 Times Cited Count:10 Percentile:65.01(Nuclear Science & Technology)

In order to investigate the effects of the experimental methodology and the notch angle on the fracture toughness of the fine-grained isotropic nuclear graphites IG-110 and IG-430, the three-point-bending test, which has been recently proposed as the methodology to evaluate the fracture toughness of graphite for high temperature gas-cooled reactors (HTGRs), was performed using two types of the specimens with different notch angles. The results obtained in this study could be summarized as follows: (1) The values of the fracture toughness of IG-110 and IG-430 measured in this study were 0.890 MPa m$$^{1/2}$$ and 1.031 MPa m$$^{1/2}$$, respectively. It was also found that the value of the fracture toughness of IG-110 was nearly equal to or smaller than the values obtained by the other method reported previously. (2) The values of the fracture toughness of the fine-grained isotropic graphites were not affected between the notch angles introduced by the incisive razor blade. (3) The ratio of the tensile strengths of IG-110 and IG-430 was estimated from Griffith Theory using the experimental data obtained in this study. The estimated strength ratio was in good agreement with the strength ratio obtained from the supplier's data.

Journal Articles

Development of evaluation method with X-ray tomography for material property of IG-430 graphite for VHTR/HTGR

Sumita, Junya; Shibata, Taiju; Fujita, Ichiro*; Kunimoto, Eiji*; Yamaji, Masatoshi*; Eto, Motokuni*; Konishi, Takashi*; Sawa, Kazuhiro

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

In this study, in order to develop evaluation method for material properties and to evaluate the irradiation-induced property changes under higher neutron doses for IG-430, the oxidation and densification effects on elastic modulus of IG-430 were investigated. Moreover, the correlation of the microstructure based on the X-ray tomography images and the material properties was discussed. It was shown that the elastic modulus of the densified graphite depends on only the closed pores and it is possible to evaluate the material properties of graphite by using X-ray tomography method. However, it is necessary to take into account of the change in the number and shape of closed pores in the grain to simulate the elastic modulus of the highly oxidized and irradiated materials by the homogenization analysis.

Journal Articles

Evaluation of fracture toughness of fine-grained isotropic graphites for HTGR

Yamada, Teruaki*; Matsushima, Yuki*; Kuroda, Masatoshi*; Sumita, Junya; Shibata, Taiju; Fujita, Ichiro*; Sawa, Kazuhiro

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

In order to investigate the effects of the experimental methodology and the notch angle on the fracture toughness of the fine-grained isotropic nuclear graphites IG-110 and IG-430, the three-point-bending test, which has been recently proposed as the methodology to evaluate the fracture toughness of graphite for high temperature gas-cooled reactors (HTGRs), was performed using two types of the specimens with different notch angles. The results obtained in this study could be summarized as follows: (1) The values of the fracture toughness of IG-110 and IG-430 measured in this study were 0.890 (MPam$$^{1/2}$$) and 1.031 (MPam$$^{1/2}$$), respectively. It was also found that the value of the fracture toughness of IG-110 was nearly equal to or smaller than the values obtained by the other method reported previously. (2) The values of the fracture toughness of the fine-grained isotropic graphites were not affected between the notch angles introduced by the incisive razor blade. (3) The ratio of the tensile strengths of IG-110 and IG-430 was estimated from Griffith Theory using the experimental data obtained in this study. The estimated strength ratio was in good agreement with the strength ratio obtained from the supplier's data.

Journal Articles

R&D plan for development of oxidation-resistant graphite and investigation of oxidation behavior of SiC coated fuel particle to enhance safety of HTGR

Ueta, Shohei; Sumita, Junya; Shibata, Taiju; Aihara, Jun; Fujita, Ichiro*; Ohashi, Jun*; Nagaishi, Yoshihide*; Muto, Takenori*; Sawa, Kazuhiro; Sakaba, Nariaki

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

A new concept of the High Temperature Gas-cooled Reactor (HTGR), so-called the Naturally Safe HTGR, is proposed as a challenge to assure no event sequences to the harmful release of radioactive materials even when the design extension conditions such as the air/water ingress accidents occur by deterministic approach based on the inherent safety features of the HTGR. For the Naturally Safe HTGR it is important to prevent recriticality accidents by keeping the geometry of the fuel rod which consists of the graphite sleeve, fuel compact and SiC-TRISO coated fuel particle, and by improving the oxidation resistance of the graphite when air/water ingress accidents occur. This paper describes the R&D plan for un-irradiation and irradiation test under simulating air/water ingress accident condition to develop oxidation-resistant graphite and to investigate the oxidation behavior of SiC coated fuel particle.

Journal Articles

Irradiation-induced dimensional change and fracture behavior of C/C composites for VHTR application

Sumita, Junya; Shibata, Taiju; Sawa, Kazuhiro; Fujita, Ichiro; Ohashi, Jun*; Takizawa, Kentaro*; Kim, W.*; Park, J.*

Ceramic Materials for Energy Applications; Ceramic Engineering and Science Proceedings, Vol.32, No.9, p.1 - 12, 2011/11

Since the temperature condition in Very High Temperature Reactor (VHTR), one of the Generation-IV reactor systems, is severe, the application of heat-resistant carbon fiber reinforced carbon matrix composite (C/C composite) for control rod elements is one of the important subjects for the VHTR development. JAEA focuses on the application of two-dimensional (2D-) C/C composites for control rod. The 2D-C/C composite has an anisotropy in properties for parallel and perpendicular to lamina directions. Irradiation effects of the 2D-C/C composite also show anisotropic behavior. It is hence important to consider the anisotropy in control rod design. To investigate the irradiation effects of the 2D-C/C composite on properties, irradiation test and post irradiation examination (PIE) were carried out and the irradiation effects were evaluated for the both directions. Since the C/C composite is composed of fibers and matrix, this geometry should be considered to evaluate the crack propagation in the composite. To assess the fracture behavior with crack propagation, bending test was carried out assuming a crack in the control rod and cracks in specimens were observed. This paper describes the irradiation effects of the 2D-C/C composite based on the PIE results considering the anisotropy. The evaluation results on equivalent fracture toughness and fracture mechanism are also discussed.

Journal Articles

Study on fracture behavior of 2D-C/C composite for application to control rod of very high temperature reactor

Sumita, Junya; Fujita, Ichiro; Shibata, Taiju; Makita, Taiyo*; Takagi, Takashi*; Kunimoto, Eiji*; Sawa, Kazuhiro; Kim, W. J.*; Park, J. Y.*

IOP Conference Series; Materials Science and Engineering, 18(16), p.162010_1 - 162010_4, 2011/09

 Times Cited Count:1 Percentile:53.13

For control rod element of Very High Temperature Reactor, carbon fiber reinforced carbon matrix composite (C/C composite) is one of the major candidate materials for its high strength and thermal stability. Since the crack propagation of the C/C composite is complicated, the fracture behavior is one of the most important subjects of the design methodology for the control rod with the C/C composite. In this study, in order to assess the Mode-II fracture behavior of the two-dimensional (2D-) C/C composite which has the layer structure of laminas composed of fibers and matrix, bending test with oxidized end notched flexure specimen was carried out. The interlaminar fracture toughness decreased with increasing the oxidation for the 2D-C/C composite. The oxidized matrix causes reduction of fracture toughness and the reduction ratio is dependent on the matrix type. The crack initiates at the boundary between fiber bundles and grows along them without breaking the fiber. It is thought that the cracks which were initiated at the interface between matrix and fiber were gathered into the voids in the boundary between fiber bundles, and then the crack grows up in the matrix.

JAEA Reports

Extrusion and erosion of bentonite buffer, 3

Matsumoto, Kazuhiro; Fujita, Tomoo

JAEA-Research 2011-014, 26 Pages, 2011/06

JAEA-Research-2011-014.pdf:1.98MB

The extrusion of bentonite buffer is one of the important issues on the physical stability in the geological disposal of the high level radiation waste. In this report, the long-term extrusion experiment of the bentonite buffer material to an imitation crack was carried out, and the behavior was observed. Moreover, in consideration of the evaluation subject of the closing performance of a disposal site, the extrusion experiment with material with a large sand combination rate was carried out.

JAEA Reports

Study of the applicability of the diffusion model of bentonite buffer material, 2

Matsumoto, Kazuhiro; Fujita, Tomoo

JAEA-Research 2010-058, 56 Pages, 2011/03

JAEA-Research-2010-058.pdf:1.73MB

Bentonite buffer material is envisaged as a component of the engineered barrier system for high-level radioactive waste disposal. As a result of its swelling property, the buffer may extrude into the surrounding host rock through open fractures. If this persists for extremely long periods of time, the buffer extrusion could lead to a reduction of buffer density, which may in turn degrade the expected performance. In this report, verification of the solid phase diffusion theory of the past was performed and future problems were extracted based on expertise.

Journal Articles

Charge-induced vortex lattice instability

Mounce, A. M.*; Oh, S.*; Mukhopadhyay, S.*; Halperin, W. P.*; Reyes, A. P.*; Kuhns, P. L.*; Fujita, Kazuhiro*; Ishikado, Motoyuki; Uchida, Shinichi*

Nature Physics, 7(2), p.125 - 128, 2011/02

 Times Cited Count:7 Percentile:47.47(Physics, Multidisciplinary)

It has been predicted that superconducting vortices should be electrically charged and that this effect is particularly enhanced for high-temperature superconductors. Hall effect and nuclear magnetic resonance (NMR) experiments suggest the existence of charge accumulation in the vortex core, but the effects are small and the interpretation controversial. Here we show that the Abrikosov vortex lattice, characteristic of the mixed state of superconductors, will become unstable at a sufficiently high magnetic field if there is charge trapped on the vortex core. Our NMR measurements of the magnetic fields generated by vortices in Bi$$_{2}$$Sr$$_{2}$$CaCu$$_{2}$$O$$_{8+y}$$ single crystals provide evidence for an electrostatically driven vortex lattice reconstruction with the magnitude of charge on each vortex pancake of $$sim2 times 10^{-3}e$$, depending on doping, in line with theoretical estimates.

Journal Articles

Spin-density wave near the vortex cores in the high-temperature superconductor Bi$$_{2}$$Sr$$_{2}$$CaCu$$_{2}$$O$$_{8+y}$$

Mounce, A. M.*; Oh, S.*; Mukhopadhyay, S.*; Halperin, W. P.*; Reyes, A. P.*; Kuhns, P. L.*; Fujita, Kazuhiro*; Ishikado, Motoyuki; Uchida, Shinichi*

Physical Review Letters, 106(5), p.057003_1 - 057003_4, 2011/02

 Times Cited Count:8 Percentile:50.98(Physics, Multidisciplinary)

Competition with magnetism is at the heart of high-temperature superconductivity, most intensely felt near a vortex core. To investigate vortex magnetism we have developed a spatially resolved probe based upon NMR spin-lattice-relaxation spectroscopy. With this approach we have found a spin-density wave associated with the vortex core in Bi$$_{2}$$Sr$$_{2}$$CaCu$$_{2}$$O$$_{8+y}$$, similar to checkerboard patterns in the local density of electronic states reported from scanning tunneling microscope experiments. We have determined both the spin-modulation amplitude and decay length from the vortex core in fields up to $$H$$ = 30 T.

Journal Articles

$$mu$$SR study of an layered organic superconductor $$kappa$$-(BEDT-TTF)$$_4$$Hg$$_{2.89}$$Br$$_8$$

Sato, Kazuhiko*; Fujita, Hidemi*; Katayama, Kazuhiro*; Taniguchi, Hiromi*; Ito, Takashi; Oishi, Kazuki*; Higemoto, Wataru

Physica B; Condensed Matter, 404(5-7), p.597 - 599, 2009/04

 Times Cited Count:4 Percentile:21.44(Physics, Condensed Matter)

Zero-field muon spin relaxation and high-field transverse muon spin rotation have been measured for an organic superconductor $$kappa$$-(BEDT-TTF)$$_4$$Hg$$_{2.89}$$Br$$_8$$. No anomaly is found in zero-field relaxation spectrum at the superconducting transition temperature, 4.2 K. The muon Knight shift determined by transverse muon spin rotation at 6 T exhibits Curie-Weiss like behavior down to 2 K, whereas static magnetic susceptibility shows a peak around 30 K. The muon Knight shift does not scale with the magnetic susceptibility at low temperatures.

Journal Articles

Enhancement of the superconducting critical temperature in Bi$$_2$$Sr$$_2$$CaCu$$_2$$O$$_{8+delta}$$ by controlling disorder outside CuO$$_2$$ planes

Hobo, Hiroaki*; Ishida, Shigeyuki*; Fujita, Kazuhiro*; Ishikado, Motoyuki; Kojima, Kenji*; Eisaki, Hiroshi*; Uchida, Shinichi*

Physical Review B, 79(6), p.064507_1 - 064507_6, 2009/02

 Times Cited Count:35 Percentile:77.13(Materials Science, Multidisciplinary)

We investigate the effect of disorder at various lattice sites outside the CuO$$_{2}$$ plane on the superconducting critical temperature $$T$$$$_{rm c}$$ of the cuprate superconductor Bi$$_2$$Sr$$_2$$CaCu$$_2$$O$$_{8+delta}$$ (Bi2212). The most effective disorder turns out to be that at the Sr site in the neighboring blocks, which contain apical-oxygen atoms.

Journal Articles

Development of a pyrochemical process in molten salts for treating radioactive waste from nuclear fuel cycle facilities

Fujita, Reiko*; Nakamura, Hitoshi*; Mizuguchi, Koji*; Utsunomiya, Kazuhiro*; Amamoto, Ippei

Proceedings of 2008 Joint Symposium on Molten Salts (USB Flash Drive), p.886 - 891, 2008/10

Pyrochemical treatment in molten salts is a promising process for decontamination of radioactive wastes without producing large amounts of secondary waste. In this report, the fundamental experiment was carried out to treat the wastes which had complicated shapes such as Magnoxend corps, metallic waste contaminated by uranium, spent chemical trap fillers and spent Zircaloy channel boxs from BWR and acquired good results.

Journal Articles

Ferritic insertion for reduction of toroidal magnetic field ripple on JT-60U

Shinohara, Koji; Sakurai, Shinji; Ishikawa, Masao; Tsuzuki, Kazuhiro*; Suzuki, Yutaka; Masaki, Kei; Naito, Osamu; Kurihara, Kenichi; Suzuki, Takahiro; Koide, Yoshihiko; et al.

Nuclear Fusion, 47(8), p.997 - 1004, 2007/08

 Times Cited Count:40 Percentile:78.58(Physics, Fluids & Plasmas)

Ferritic steel plates have been installed to improve the energetic ion confinement through reducing a toroidal magnetic field ripple. Aiming at cost-effective installation, orbit following calculations of energetic ions were performed for a design of ferritic installation on JT-60U by using the Fully three Dimensional magnetic field Orbit-Following Monte-Carlo (F3D OFMC) code. The installed ferritic steel adds the non-linear magnetic field on magnetic sensors for a plasma control and an equilibrium calculation. The code for a real-time control has been modified to take into account the magnetic field by ferritic steel. The plasma operation was successfully resumed and a real-time plasma control was successfully carried out after usual preparation processes. The heat load measurement indicates the improved confinement of energetic ions. These results are important for practical application of ferritic steel which is a leading candidate of a structural material on a demo reactor.

Journal Articles

Ferritic insertion for reduction of toroidal magnetic field ripple on JT-60U

Shinohara, Koji; Sakurai, Shinji; Ishikawa, Masao; Tsuzuki, Kazuhiro*; Suzuki, Yutaka; Masaki, Kei; Naito, Osamu; Kurihara, Kenichi; Suzuki, Takahiro; Koide, Yoshihiko; et al.

Proceedings of 21st IAEA Fusion Energy Conference (FEC 2006) (CD-ROM), 8 Pages, 2007/03

Ferritic steel plates have been installed to improve the energetic ion confinement through reducing a toroidal magnetic field ripple. Aiming at cost-effective installation, orbit following calculations of energetic ions were performed for a design of ferritic installation on JT-60U by using the Fully three Dimensional magnetic field Orbit-Following Monte-Carlo (F3D OFMC) code. The installed ferritic steel adds the non-linear magnetic field on magnetic sensors for a plasma control and an equilibrium calculation. The code for a real-time control have been modified to take into account the magnetic field by ferritic steel. The plasma operation was successfully resumed and a real-time plasma control was successfully carried out after usual preparation processes. The heat load measurement indicates the improved confinement of energetic ions. These results are important for practical application of ferritic steel which is a leading candidate of a structural material on a demo reactor.

JAEA Reports

The Study plan on applicability to actual geological environment conditions of the engineering technology for geological disposal of high level nuclear-waste through the second phases in Horonobe Underground Research Project

Aoyanagi, Shigeo; Yui, Mikazu; Tanai, Kenji; Kawakami, Susumu; Fujita, Tomoo; Taniguchi, Naoki; Shibata, Masahiro; Konishi, Kazuhiro; Nishimura, Mayuka; Kikuchi, Hirohito*; et al.

JAEA-Review 2006-014, 61 Pages, 2006/03

JAEA-Review-2006-014.pdf:5.03MB

no abstracts in English

Journal Articles

Study of global wall saturation mechanisms in long-pulse ELMy H-mode discharges on JT-60U

Takenaga, Hidenobu; Nakano, Tomohide; Asakura, Nobuyuki; Kubo, Hirotaka; Konoshima, Shigeru; Shimizu, Katsuhiro; Tsuzuki, Kazuhiro; Masaki, Kei; Tanabe, Tetsuo*; Ide, Shunsuke; et al.

Nuclear Fusion, 46(3), p.S39 - S48, 2006/03

 Times Cited Count:18 Percentile:52.6(Physics, Fluids & Plasmas)

no abstracts in English

40 (Records 1-20 displayed on this page)