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Journal Articles

Overview of event progression of evaporation to dryness caused by boiling of high-level liquid waste in Reprocessing Facilities

Yamaguchi, Akinori*; Yokotsuka, Muneyuki*; Furuta, Masayo*; Kubota, Kazuo*; Fujine, Sachio*; Mori, Kenji*; Yoshida, Naoki; Amano, Yuki; Abe, Hitoshi

Nihon Genshiryoku Gakkai Wabun Rombunshi (Internet), 21(4), p.173 - 182, 2022/09

Risk information obtained from probabilistic risk assessment (PRA) can be used to evaluate the effectiveness of measures against severe accidents in nuclear facilities. The PRA methods used for reprocessing facilities are considered immature compared to those for nuclear power plants, and to make the methods mature, reducing the uncertainty of accident scenarios becomes crucial. In this paper, we summarized the results of literature survey on the event progression of evaporation to dryness caused by boiling of high-level liquid waste (HLLW) which is a severe accident in reprocessing facilities and migration behavior of associated radioactive materials. Since one of the important characteristics of Ru is its tendency to form volatile compounds over the course of the event progression, the migration behavior of Ru is categorized into four stages based on temperature. Although no Ru has been released in the waste in the high temperature region, other volatile elements such as Cs could be released. Sufficient experimental data, however, have not been obtained yet. It is, therefore, necessary to further clarify the migration behavior of radioactive materials that predominantly depends on temperature in this region.

Journal Articles

Development of methodology to evaluate mechanical consequences of vapor expansion in SFR severe accident transients; Lessons learned from previous France-Japan collaboration and future objectives and milestones

Bachrata, A.*; Gentet, D.*; Bertrand, F.*; Marie, N.*; Kubota, Ryuzaburo*; Sogabe, Joji; Sasaki, Keisuke; Kamiyama, Kenji; Yamano, Hidemasa; Kubo, Shigenobu

Proceedings of International Conference on Fast Reactors and Related Fuel Cycles; Sustainable Clean Energy for the Future (FR22) (Internet), 9 Pages, 2022/04

In the frame of France-Japan collaboration, one of the objectives is to define and assess the calculation methodologies, and to investigate the phenomenology and the consequences of severe accident scenarios in sodium fast reactors (SFRs). A methodology whose purpose is to assess the loadings of the structures induced by a Fuel Coolant Interaction (FCI) taking place in the sodium plenum of SFR has been defined in the frame of the collaboration between France and Japan during 2014-2019. The work progress will be spread over the period 2020-2024 and the main objectives and milestones will be introduced in the paper. The objective of studies is to comprehensively address the margin between the limit of integrity of the main vessel structures and the loadings resulting from severe accidents. For this purpose, the SIMMER mechanistic calculation code simulates core disruptive accident sequences in SFRs. A fluid structure dynamics tool evaluates this interaction i.e. EUROPLEXUS is used in CEA studies and AUTODYN tool is used in JAEA studies. In the paper, a benchmark study is described in order to illustrate the evaluation of vapour expansion phase in the hot plenum. To do that, joint input data are used on the basis of an ASTRID 1500 MWth core degraded state after the power excursion which leads to vapour expansion. The most penalizing case was evidenced in this study by suppressing the action of transfer tube in-core mitigation devices in SIMMER input deck and thus privileging the upward molten core ejection. Even if the most penalizing case was evidenced in this paper, no significant RV deformation was observed in both EUROPLEXUS and AUTODYN calculation results. The assumed mechanical energy was small for the core expansion phase.

Journal Articles

Formation of $$alpha$$ clusters in dilute neutron-rich matter

Tanaka, Junki*; Yang, Z.*; Typel, S.*; Adachi, Satoshi*; Bai, S.*; van Beek, P.*; Beaumel, D.*; Fujikawa, Yuki*; Han, J.*; Heil, S.*; et al.

Science, 371(6526), p.260 - 264, 2021/01

 Times Cited Count:30 Percentile:99.14(Multidisciplinary Sciences)

By employing quasi-free $$alpha$$-cluster-knockout reactions, we obtained direct experimental evidence for the formation of $$alpha$$ clusters at the surface of neutron-rich tin isotopes. The observed monotonous decrease of the reaction cross sections with increasing mass number, in excellent agreement with the theoretical prediction, implies a tight interplay between $$alpha$$-cluster formation and the neutron skin.

Journal Articles

Evaluation of the excavation disturbed zone of sedimentary rock in the Horonobe Underground Research Laboratory

Kubota, Kenji*; Aoyagi, Kazuhei; Sugita, Yutaka

Proceedings of 2019 Rock Dynamics Summit in Okinawa (USB Flash Drive), p.729 - 733, 2019/05

During the excavation of shafts and galleries in the deep subsurface for disposing of high-level radioactive waste, an excavation disturbed zone (EdZ) or excavation damaged zone (EDZ) is developed around the shafts and galleries. Such zones could influence the transfer behavior of radioactive nuclides, and it is therefore important to understand the behavior of the EdZ or EDZ. We performed in situ experiments before, during, and after gallery excavation in galleries of 140 and 250 m in depth in an area of soft sedimentary rock in Japan. The results demonstrate that the extent of fractures induced by the gallery excavation related with EDZ was confined to about 0.45 m from the gallery wall in the 140 m gallery and to about 1 m from the gallery wall in the 250 m gallery. The extent of the unsaturated zone related with EdZ was about 1 m in the 140 m gallery, but an unsaturated zone did not appear in the 250 m gallery.

JAEA Reports

A Study of the evaluation of the excavation damaged zone in the Horonobe Underground Research Laboratory, 1; Investigation in the 140 m gallery (Joint research)

Sugita, Yutaka; Aoyagi, Kazuhei; Kubota, Kenji*; Nakata, Eiji*; Oyama, Takahiro*

JAEA-Research 2018-002, 72 Pages, 2018/06

JAEA-Research-2018-002.pdf:6.16MB

In a excavation of shafts and galleries in the deep underground for disposing radioactive waste, an excavation damaged zone (EDZ) is developed around the galleries and shafts owing to the stress redistribution. Since the characteristic changes of the rock mass in the EDZ affects the radionuclides migration behavior, it is important to understand the long-term behavior of the EDZ. Thus, we performed the in situ experiment to investigate the long-term behavior of EDZ as part of the collaborative research between Japan Atomic Energy Agency and Central Research Institute of Electric Power Industry in the 140m gallery in the Horonobe Underground Research Laboratory. In this research, we investigated the extent, mechanism of the change of hydro-mechanical characteristic, and long-term behavior of the EDZ on the basis of the comprehensive estimation of the results of the observation of the drift wall and the various investigations using boreholes such as geological investigation, the seismic and resistivity tomography, hydraulic test, water content monitoring, borehole loading test, convergence measurement, and so on. In addition, we clarified applicability and future tasks of the testing method used in this research for the investigation of the long-term behavior of the EDZ.

Journal Articles

Investigation of the excavation disturbed zone due to the excavation of horizontal galleries; Study in the Horonobe Underground Research Laboratory

Kubota, Kenji*; Aoyagi, Kazuhei; Sugita, Yutaka

Koeki Shadan Hojin Butsuri Tansa Gakkai Dai-138-Kai (Heisei-30-Nendo Shuki) Gakujutsu Koenkai Koen Rombunshu, p.51 - 54, 2018/05

In an excavation of shafts and galleries in the deep underground for disposing high level radioactive waste, an excavation disturbed zone (EdZ) or excavation damaged zone (EDZ) is developed around the shafts and galleries owing to the stress redistribution. It is important to understand the behavior of the EdZ or EDZ because these zone could have an effect on the transfer behavior of radioactive nuclide. Therefore, the authors performed the in situ experiment to investigate the behavior of EdZ or EDZ in the 140m and 250m gallery in the Horonobe Underground Research Laboratory. From the result of the experiments, the authors compared the characteristics of EdZ or EDZ between those in 140m and 250m gallery. The extent of the fractures induced by the gallery excavation, i.e., EDZ was about 0.45m in the 140m gallery and about 1m in the 250m gallery. The extent of the unsaturated zones related with EdZ was about 1m in the 140m gallery, however, unsaturated zone was not appeared in the 250m gallery.

JAEA Reports

A Study of the evaluation of the excavation damaged zone in the Horonobe Underground Research Laboratory, 2; Investigation in the 250 m gallery (Joint research)

Aoyagi, Kazuhei; Kubota, Kenji*; Nakata, Eiji*; Suenaga, Hiroshi*; Nohara, Shintaro*

JAEA-Research 2017-004, 91 Pages, 2017/06

JAEA-Research-2017-004.pdf:6.07MB

In this study, we performed seismic tomography, seismic refraction survey, resistivity tomography, and hydraulic tests to investigate the hydro-mechanical property of the excavation damaged zone (EDZ) in the 250 m gallery of the Horonobe Underground Research Laboratory. As a result of seismic tomography, seismic velocity is significantly decreased within 1 m from the gallery wall. The decrease of seismic velocity is related to the density of fracture induced around the gallery wall as a result of the gallery excavation. Thus the extent of the fractures induced by gallery excavation, i.e., EDZ fractures is clarified to be within 1.0 m from the gallery wall. The enhanced hydraulic conductivity was detected within 0.5 to 1.0 m from the gallery wall on the basis of the result of hydraulic tests. This is almost consistent with the extent of the region that seismic velocity is significantly decreased. Therefore, it is estimated that EDZ fractures induced around the gallery leads to the increase of hydraulic conductivity. In addition, the desaturation zone around the gallery is not induced as a result of resistivity tomography. From these results, the hydro-mechanical property of the EDZ is clarified in detail. Also, the in situ tests and evaluation method applied in this study are appropriate to investigate the EDZ in detail.

JAEA Reports

Decommissioning activities and R&D of nuclear facilities in the second midterm plan

Terunuma, Akihiro; Mimura, Ryuji; Nagashima, Hisao; Aoyagi, Yoshitaka; Hirokawa, Katsunori*; Uta, Masato; Ishimori, Yuu; Kuwabara, Jun; Okamoto, Hisato; Kimura, Yasuhisa; et al.

JAEA-Review 2016-008, 98 Pages, 2016/07

JAEA-Review-2016-008.pdf:11.73MB

Japan Atomic Energy Agency formulated the plan to achieve the medium-term target in the period of April 2010 to March 2015(hereinafter referred to as "the second medium-term plan"). JAEA determined the plan for the business operations of each year (hereinafter referred to as "the year plan"). This report is that the Sector of Decommissioning and Radioactive Waste Management has summarized the results of the decommissioning technology development and decommissioning of nuclear facilities which were carried out in the second medium-term plan.

Journal Articles

Investigations for av change of an excavation damaged zone with time at the 250 m gallery in the Horonobe Underground Research Laboratory

Aoyagi, Kazuhei; Tsusaka, Kimikazu; Kubota, Kenji*; Tokiwa, Tetsuya; Kondo, Keiji; Inagaki, Daisuke

Doboku Gakkai Rombunshu, C (Chiken Kogaku) (Internet), 70(4), p.412 - 423, 2014/12

The authors have been conducting seismic and resistivity tomography surveys in a gallery of the Horonobe Underground Research Laboratory in order to investigate an extent of an excavation damaged zone (EDZ) along time. The objective of this paper is to discuss an influence of fracture distribution and water saturation of a rock mass on variations in seismic velocity and the value of apparent resistivity in an EDZ. Based on the result of seismic tomography survey, the extent of a layer which has low seismic velocity was about 1.0 m from the gallery wall after excavation of the tomography area. From the results of resistivity tomography survey, the value of apparent resistivity has not changed remarkably along time. To investigate a relationship between variations in seismic velocity and density of fracture in the survey area, the authors built a three dimensional fracture model around the tomography area. From the comparison of seismic velocity with density of fracture, seismic velocity decreased almost linearly as the density of fracture increased. Also, it was found that density of fracture in the layer of low seismic velocity could be estimated using a simple numeric model. From this result, seismic tomography survey and investigation of density of fracture are suitable method for evaluation of an EDZ.

Journal Articles

Hydrogeomechanical investigation of an excavation damaged zone in the Horonobe Underground Research Laboratory

Aoyagi, Kazuhei; Tsusaka, Kimikazu*; Nohara, Shintaro*; Kubota, Kenji*; Tokiwa, Tetsuya*; Kondo, Keiji*; Inagaki, Daisuke*

Proceedings of 8th Asian Rock Mechanics Symposium (ARMS-8) (USB Flash Drive), 8 Pages, 2014/10

Journal Articles

Fractures distribution around underground gallery in sedimentary rock area

Nohara, Shintaro*; Nakata, Eiji*; Suenaga, Hiroshi*; Tanaka, Shiro*; Kubota, Kenji*; Oyama, Takahiro*; Kondo, Keiji

Nihon Oyo Chishitsu Gakkai Heisei-25-Nendo Kenkyu Happyokai Koen Rombunshu, p.129 - 130, 2013/10

no abstracts in English

Journal Articles

Monitoring of the excavation damaged zone (EDZ) by geophysical methods during the test tunnel excavation at a depth of 140 m and 250 m

Kubota, Kenji*; Kondo, Keiji; Sakakibara, Junichi*

Shadan Hojin Butsuri Tansa Gakkai Dai-128-Kai (Heisei-25-Nendo Shuki) Gakujutsu Koenkai Koen Rombunshu, p.62 - 65, 2013/06

To evaluate the excavated damaged zone (EDZ) is one of the important factors to conduct high level radioactive waste disposal. We have conducted resistivity and acoustic tomography to evaluate EDZ during the excavation of the test tunnel at a depth of 140 m and 250 m. As a result, a few meters extent of high resistivity and low P-wave velocity zone were detected at a depth of 140 m. This suggests that EDZ by excavation of horizontal tunnel was estimated by resistivity and acoustic tomography. On the other hand, high resistivity zone were not detected at a depth of 250 m.

Journal Articles

A Study on flow field of purge gas for tritium transfer through breeder pebble bed in fusion blanket

Seki, Yohji; Ezato, Koichiro; Yokoyama, Kenji; Enoeda, Mikio; Kubota, Jinichi*; Sakamoto, Kensaku

Proceedings of 8th Japan-Korea Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS-8) (USB Flash Drive), 8 Pages, 2012/12

Japan Atomic Energy Agency has been performing R&D and design of a blanket module of a nuclear fusion reactor. Pebbles of a ceramic tritium breeder are packed in a container of the blanket. Helium purge gas is applied as a transport fluid in a tritium recovery system. Prediction of the flow phenomena with a tritium transfer is important for designs of the container. A purpose of our research is to establish and verify a method for a prediction of the flow in the pebble bed. In this study, pressure drops of the helium purge gas through the pebble bed were measured up to 100 L/min of flow rate. Reliability of prediction ability of the pressure drop was validated by this experiment within the flow rate which is less than 40 L/min. A numerical simulation for the flow field through the pebble bed also has been performed. Consequently, the velocity distributions are quantitatively and qualitatively obtained at near the wall and the center region in the pebble bed.

Journal Articles

Actinide-handling experience for training and education of future expert under J-ACTINET

Osaka, Masahiko; Konashi, Kenji*; Hayashi, Hirokazu; Li, D.*; Homma, Yoshiya*; Yamamura, Tomoo*; Sato, Isamu; Miwa, Shuhei; Sekimoto, Shun*; Kubota, Takumi*; et al.

Proceedings of International Conference on Toward and Over the Fukushima Daiichi Accident (GLOBAL 2011) (CD-ROM), 5 Pages, 2011/12

Summer schools for future experts have successfully been completed under Japan Actinide Network (J-ACTINET) for the purpose of development of human resources who are expected to be engaged in every areas of actinide-research/engineering. The first summer school was held in Ibaraki-area in August 2009, followed by the second one in Kansai-area in August 2010. Two summer schools have focused on actual experiences of actinides in actinide-research fields for university students and young researchers/engineers as an introductory course of actinide-researches. Several quasi actinide-handling experiences at the actinide-research fields have attracted attentions of participants at the first school in Ibaraki-area. The actual experiments using actinides-containing solutions have been carried out at the second school in Kansai-area. Future summer schools will be held every year for the sustainable human resource development in various actinide-research fields.

Journal Articles

Volume phase transitions of pyly(acryloyl-L-proline methyl ester) gels in response to water-alcohol composition

Hiroki, Akihiro*; Maekawa, Yasunari; Yoshida, Masaru; Kubota, Kenji*; Katakai, Ryoichi*

Polymer, 42(5), p.1863 - 1867, 2000/12

 Times Cited Count:41 Percentile:79.58(Polymer Science)

no abstracts in English

JAEA Reports

Investigation on sealing in geological disposal

Aoki, Kenji*; Hibiya, Keisuke*; Shiogama, Yukihiro*; Toida, Masaru*; Yamamoto, T.*; Yoshida, Hiroshi*; Banno, K.*; Kubota, T.*; Shimizu, Y.*; Okutsu, Kazuo*; et al.

PNC TJ1100 94-001, 69 Pages, 1994/02

PNC-TJ1100-94-001.pdf:4.56MB

None

Oral presentation

Time-lapse measurement of resistivity and acoustic tomography during the excavation of the test tunnel at a depth of 140 m

Kubota, Kenji*; Suzuki, Koichi*; Sugita, Yutaka; Sakakibara, Junichi*

no journal, , 

no abstracts in English

Oral presentation

Charge ordering state in the electronic ferroelectric LuFe$$_{2}$$O$$_{4}$$ studied by use of synchrotron radiation

Kubota, Masato*; Hayakawa, Hironori*; Oishi, Daisuke*; Akahama, Yuji*; Yoshii, Kenji; Kambe, Takashi*; Ikeda, Naoshi*

no journal, , 

Charge-ordered state of electronic ferroelectric LuFe$$_{2}$$O$$_{4}$$ was studied by use of synchrotron radiation. We have performed X-ray diffraction measurements at Fe K- and L-edges for a single-crystal LuFe$$_{2}$$$$_{4}$$ with applying currents at around room temperature. It was observed that the charge-ordered state changed depending on parameters such as the current density and the direction of current. We will discuss detailed results of experiments and at the conference.

Oral presentation

Applied-electric-field dependence of charge ordered phase in the trianglular-lattice system LuFe$$_{2}$$O$$_{4}$$

Hayakawa, Hironori*; Kubota, Masato*; Oishi, Daisuke*; Akahama, Yuji*; Matsuo, Yoji*; Ikeda, Naoshi*; Kambe, Takashi*; Kimizuka, Noboru*; Yoshii, Kenji

no journal, , 

We have investigated the change of charge-ordered state in LuFe$$_{2}$$O$$_{4}$$ caused by an applied electric field. The application of the field above a threshold led to a drastic decrease in resistivity; this behavior corresponds to the change of charge-ordered structure observed using synchrotron radiation. More details will be shown at the conference.

Oral presentation

Inelastic neutron scattering study on phonon spectra in dimer-Mott insulator $$beta^{prime}$$-(BEDT-TTF)$$_2$$ICl$$_2$$

Kawamura, Seiko; Matsuura, Masato*; Iguchi, Satoshi*; Sasaki, Takahiko*; Taniguchi, Hiromi*; Kubota, Aiko*; Sato, Kazuhiko*; Inamura, Yasuhiro; Kikuchi, Tatsuya; Kawakita, Yukinobu; et al.

no journal, , 

A molecular dimer-Mott insulator $$beta^{prime}$$-(BEDT-TTF)$$_2$$ICl$$_2$$ is a candidate for a new type of ferroelectric system which shows a relaxor-like dielectric response. We performed inelastic neutron scattering measurements on this system by using a chopper specrometer, and observed phonon spectra in a wide wave vector ($$Q$$)-energy ($$E$$) region for the first time. Clear optical modes with the energies up to $$sim$$ 36 meV were observed together with an acoustic phonon dispersion. The intensity of the optical mode with the lowest energy $$E$$ = 4.2 meV increases at a zone boundary along the $$b$$* axis below $$T_{FE}$$ = 62 K, at which a glassy ferroelectricity appears, and it further increases all over the measured $$Q$$ range below the antiferromangetic transition temperature $$T_{rm N}$$ = 22 K. The results suggest that the lattice dynamics characterized by this optical phonon mode is significantly coupled with strongly correlated charge and spin degrees of freedom.

27 (Records 1-20 displayed on this page)