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Journal Articles

Production of $$^{266}$$Bh in the $$^{248}$$Cm($$^{23}$$Na,5$$n$$)$$^{266}$$Bh reaction and its decay properties

Haba, Hiromitsu*; Fan, F.*; Kaji, Daiya*; Kasamatsu, Yoshitaka*; Kikunaga, Hidetoshi*; Komori, Yukiko*; Kondo, Narumi*; Kudo, Hisaaki*; Morimoto, Koji*; Morita, Kosuke*; et al.

Physical Review C, 102(2), p.024625_1 - 024625_12, 2020/08

 Times Cited Count:2 Percentile:57.67(Physics, Nuclear)

Journal Articles

Development of inspection and repair techniques in reactor vessel of experimental fast reactor "Joyo"; Retrieval of the bent test subassembly

Ashida, Takashi; Ito, Hideaki; Miyamoto, Kazuyuki*; Nakamura, Toshiyuki; Koga, Kazuhiro*; Ohara, Norikazu*; Ino, Hiroichi*

Nihon Genshiryoku Gakkai Wabun Rombunshi, 15(4), p.210 - 222, 2016/12

In the experimental fast reactor Joyo, it was confirmed that the top of the irradiation test sub-assembly of material testing rig named "MARICO-2" had been broken and bent onto the in-vessel storage rack as an obstacle and had damaged the upper core structure (UCS). As the result, for Joyo restart, it was necessary to replace the damaged UCS and to retrieve the bent sub-assembly. This paper describes in-vessel repair techniques performed in the retrieval work of the obstacle inside of the reactor vessel. The devices which were prepared for this work demonstrated expected performance under the environmental conditions of an SFR such as high temperature and radiation dose, and the work was completed in 2014. The successful operation of this retrieval work of the damaged component inside of a reactor vessel will contribute to the development of in-service inspections and repair technics in an SFR.

Journal Articles

Investigation of countermeasure against local temperature rise in vessel cooling system in loss of core cooling test without nuclear heating

Ono, Masato; Shimizu, Atsushi; Kondo, Makoto; Shimazaki, Yosuke; Shinohara, Masanori; Tochio, Daisuke; Iigaki, Kazuhiko; Nakagawa, Shigeaki; Takada, Shoji; Sawa, Kazuhiro

Journal of Nuclear Engineering and Radiation Science, 2(4), p.044502_1 - 044502_4, 2016/10

In the loss of forced core cooling test using High Temperature engineering Test Reactor (HTTR), the forced cooling of reactor core is stopped without inserting control rods into the core and cooling by Vessel Cooling System (VCS) to verify safety evaluation codes to investigate the inherent safety of HTGR be secured by natural phenomena to make it possible to design a severe accident free reactor. The VCS passively removes the retained residual heat and the decay heat from the core via the reactor pressure vessel by natural convection and thermal radiation. In the test, the local temperature was supposed to exceed the limit from the viewpoint of long-term use at the uncovered water cooling tube by thermal reflectors in the VCS, although the safety of reactor is kept. Through a cold test, which was carried out by non-nuclear heat input from gas circulators with stopping water flow in the VCS, the local higher temperature position was specified although the temperature was sufficiently lower than the maximum allowable working temperature, and natural circulation of water had insufficient cooling effect on the temperature of water cooling tube below 1$$^{circ}$$C. Then, a new safe and secured procedure for the loss of forced core cooling test was established, which will be carried out soon after the restart of HTTR.

Journal Articles

Development of the prediction technology of cable disconnection of in-core neutron detector for the future high-temperature gas-cooled reactors

Shimazaki, Yosuke; Sawahata, Hiroaki; Kawamoto, Taiki; Suzuki, Hisashi; Shinohara, Masanori; Honda, Yuki; Katsuyama, Kozo; Takada, Shoji; Sawa, Kazuhiro

Journal of Nuclear Engineering and Radiation Science, 2(4), p.041008_1 - 041008_5, 2016/10

Maintenance technologies for the reactor system have been developed by using the high-temperature engineering test reactor (HTTR). One of the important purposes of development is to accumulate the experiences and data to satisfy the availability of operation up to 90% by shortening the duration of the periodical maintenance for the future HTGRs by shifting from the time-based maintenance to condition-based maintenance. The technical issue of the maintenance of in-core neutron detector, wide range monitor (WRM), is to predict the malfunction caused by cable disconnection to plan the replacement schedule. This is because that it is difficult to observe directly inside of the WRM in detail. The electrical inspection method was proposed to detect and predict the cable disconnection of the WRM by remote monitoring from outside of the reactor by using the time domain reflectometry and so on. The disconnection position, which was specified by the electrical method, was identified by non-destructive and destructive inspection. The accumulated data is expected to be contributed for advanced maintenance of future HTGRs.

Journal Articles

Femtosecond time-resolved dynamical Franz-Keldysh effect

Otobe, Tomohito; Shinohara, Yasushi*; Sato, Shunsuke*; Yabana, Kazuhiro*

Physical Review B, 93(4), p.045124_1 - 045124_9, 2016/01

 Times Cited Count:34 Percentile:86.73(Materials Science, Multidisciplinary)

We theoretically investigate the dynamical Franz-Keldysh effect in femtosecond time resolution, that is, the time-dependent modulation of a dielectric function at around the band gap under an irradiation of an intense laser field. We develop a pump-probe formalism in two distinct approaches: first-principles simulation based on real-time time-dependent density functional theory and analytic consideration of a simple two-band model. We find that, while time-average modulation may be reasonably described by the static Franz-Keldysh theory, a remarkable phase shift is found to appear between the dielectric response and the applied electric field.

Journal Articles

Preparation and evaluation of an astatine-211-labeled sigma receptor ligand for $$alpha$$ radionuclide therapy

Ogawa, Kazuma*; Mizuno, Yoshiaki*; Washiyama, Koshin*; Shiba, Kazuhiro*; Takahashi, Naruto*; Kozaka, Takashi*; Watanabe, Shigeki; Shinohara, Atsushi*; Odani, Akira*

Nuclear Medicine and Biology, 42(11), p.875 - 879, 2015/11

 Times Cited Count:18 Percentile:69.85(Radiology, Nuclear Medicine & Medical Imaging)

Journal Articles

Time-dependent density functional theory of high-intensity short-pulse laser irradiation on insulators

Sato, Shunsuke*; Yabana, Kazuhiro*; Shinohara, Yasushi*; Otobe, Tomohito; Lee, K.-M.*; Bertsch, G. F.*

Physical Review B, 92(20), p.205413_1 - 205413_6, 2015/11

 Times Cited Count:33 Percentile:83.54(Materials Science, Multidisciplinary)

We calculate the energy deposition by very short laser pulses in SiO$$_{2}$$ ($$alpha$$-quartz) with a view to establishing systematics for predicting damage and nanoparticle production. The theoretical framework is time-dependent density functional theory, implemented by the real-time method in a multiscale representation. We find that the deposited energy in the medium can be accurately modeled as a function of the local electromagnetic pulse fluence. The energy deposition function can in turn be quite well fitted to the strong-field Keldysh formula. We find reasonable agreement between the damage threshold and the energy required to melt the substrate. The ablation threshold estimated by the energy to convert the substrate to an atomic fluid is higher than the measurement, indicating significance of nonthermal nature of the process. A fair agreement is found for the depth of the ablation.

Journal Articles

Experimental fast reactor "JOYO" retrieval for the bent MARICO-2 test subassembly using remote control devices

Koga, Kazuhiro*; Ohara, Norikazu*; Ino, Hiroichi*; Kondo, Katsumi*; Ito, Hideaki; Ashida, Takashi; Nakamura, Toshiyuki

FAPIG, (190), p.3 - 8, 2015/07

no abstracts in English

Journal Articles

Proton order-disorder phenomena in a hydrogen-bonded rhodium-$$eta$$$$^{5}$$-semiquinone complex; A Possible dielectric response mechanism

Mitsumi, Minoru*; Ezaki, Kazunari*; Komatsu, Yuki*; Toriumi, Koshiro*; Miyato, Tatsuya*; Mizuno, Motohiro*; Azuma, Nobuaki*; Miyazaki, Yuji*; Nakano, Motohiro*; Kitagawa, Yasutaka*; et al.

Chemistry; A European Journal, 21(27), p.9682 - 9696, 2015/06

 Times Cited Count:6 Percentile:26.76(Chemistry, Multidisciplinary)

Journal Articles

Development of the prediction technology of cable disconnection of in-core neutron detector for the future high-temperature gas cooled reactors

Shimazaki, Yosuke; Sawahata, Hiroaki; Kawamoto, Taiki; Suzuki, Hisashi; Shinohara, Masanori; Honda, Yuki; Katsuyama, Kozo; Takada, Shoji; Sawa, Kazuhiro

Proceedings of 23rd International Conference on Nuclear Engineering (ICONE-23) (DVD-ROM), 7 Pages, 2015/05

Maintenance technologies for the reactor system have been developed by using the high-temperature engineering test reactor (HTTR). One of the important purposes of development is to accumulate the experiences and data to satisfy the availability of operation up to 90% by shortening the duration of the periodical maintenance for the future HTGRs by shifting from the time-based maintenance to condition-based maintenance. The technical issue of the maintenance of in-core neutron detector, wide range monitor (WRM), is to predict the malfunction caused by cable disconnection to plan the replacement schedule. This is because that it is difficult to observe directly inside of the WRM in detail. The electrical inspection method was proposed to detect and predict the cable disconnection of the WRM by remote monitoring from outside of the reactor by using the time domain reflectometry and so on. The disconnection position, which was specified by the electrical method, was identified by non-destructive and destructive inspection. The accumulated data is expected to be contributed for advanced maintenance of future HTGRs.

Journal Articles

Investigation of characteristics of natural circulation of water in vessel cooling system in loss of core cooling test without nuclear heating

Takada, Shoji; Shimizu, Atsushi; Kondo, Makoto; Shimazaki, Yosuke; Shinohara, Masanori; Seki, Tomokazu; Tochio, Daisuke; Iigaki, Kazuhiko; Nakagawa, Shigeaki; Sawa, Kazuhiro

Proceedings of 23rd International Conference on Nuclear Engineering (ICONE-23) (DVD-ROM), 5 Pages, 2015/05

In the loss of forced core cooling test using High Temperature engineering Test Reactor (HTTR), the forced cooling of reactor core is stopped without inserting control rods into the core and cooling by Vessel Cooling System (VCS) to demonstrate the inherent safety of HTGR be secured by natural phenomena to make it possible to design a severe accident free reactor. In the test, the local temperature was supposed to exceed the limit from the viewpoint of long-term use at the uncovered water cooling tube by thermal reflectors in the VCS, although the safety of reactor is kept. The local higher temperature position was specified although the temperature was sufficiently lower than the maximum allowable working temperature, and natural circulation of water had insufficient cooling effect on the temperature of water cooling tube below 1$$^{circ}$$C. Then, a new safe and secured procedure for the loss of forced core cooling test was established, which will be carried out soon after the restart of HTTR.

Journal Articles

Journal Articles

Dielectric response of laser-excited silicon at finite electron temperature

Sato, Shunsuke*; Shinohara, Yasushi*; Otobe, Tomohito; Yabana, Kazuhiro*

Physical Review B, 90(17), p.174303_1 - 174303_8, 2014/11

 Times Cited Count:24 Percentile:75.15(Materials Science, Multidisciplinary)

We calculate the dielectric response of excited crystalline silicon in electron thermal equilibrium by adiabatic time-dependent density functional theory (TDDFT) to model the response to irradiation by high-intensity laser pulses. We find that the extracted effective mass are in the range of 0.22-0.36 and lifetimes are in the range of 1-14 fs depending on the temperature.

Journal Articles

Near term test plan using HTTR (High Temperature engineering Test Reactor)

Takada, Shoji; Iigaki, Kazuhiko; Shinohara, Masanori; Tochio, Daisuke; Shimazaki, Yosuke; Ono, Masato; Yanagi, Shunki; Nishihara, Tetsuo; Fukaya, Yuji; Goto, Minoru; et al.

Nuclear Engineering and Design, 271, p.472 - 478, 2014/05

 Times Cited Count:5 Percentile:43.74(Nuclear Science & Technology)

JAEA has carried out research and development to establish the technical basis of HTGRs using HTTR. To connect hydrogen production system to HTTR, it is necessary to ensure the reactor dynamics when thermal-load of the system is lost. Thermal-load fluctuation test is planned to demonstrate the reactor dynamics stability and to validate plant dynamics codes. It will be confirmed that the reactor become stable state during losing a part of removed heat at heat-sink. A temperature coefficient of reactivity is one of the important parameters for core dynamics calculations, and changes with burnup because of variance of fuel compositions. Measurement of temperature coefficient of reactivity has been conducted to confirm the validity of calculated temperature coefficient of reactivity. A LOFC test using HTTR has been carried out to verify the inherent safety under the condition of LOFC while the reactor shut-down system disabled.

JAEA Reports

Proposal of safety demonstration test plan of HTTR by cold test of loss of forced cooling with vessel cooling system inactive

Takada, Shoji; Shinohara, Masanori; Seki, Tomokazu; Shimazaki, Yosuke; Ono, Masato; Tochio, Daisuke; Iigaki, Kazuhiko; Sawa, Kazuhiro

JAEA-Technology 2014-001, 34 Pages, 2014/03

JAEA-Technology-2014-001.pdf:4.46MB

The loss of forced cooling with vessel cooling system inactive has been planned by using HTTR at the reactor power 9 MW. In this test, the forced cooling of reactor core is lost and the vessel cooling system which removes decay heat from core is tripped. In the test, the technical items such that the temperature of water cooling tubes is expected to be higher are considered. The methods to solve such technical items were proposed. The proposed methods were verified based on the test data of the cold test toward the proposal of test plan of safety demonstration test. In the cold test, the two water trains of vessel cooling system was tripped under the condition that the reactor was heated up without nuclear heating. The reactor inlet temperature was set at 120 and 150$$^{circ}$$C.

Journal Articles

First-principles simulation of the optical response of bulk and thin-film $$alpha$$-quartz irradiated with an ultrashort intense laser pulse

Lee, K.-M.*; Kim, C. M.*; Sato, Shunsuke*; Otobe, Tomohito; Shinohara, Yasushi*; Yabana, Kazuhiro; Jeong, T. M.*

Journal of Applied Physics, 115(5), p.053519_1 - 053519_8, 2014/02

 Times Cited Count:22 Percentile:72.74(Physics, Applied)

A computational method based on a first-principles multiscale simulation has been used for calculating the optical response and the ablation threshold of an optical material irradiated with an ultrashort intense laser pulse. The method was applied to investigate the changes in the optical reflectance of quartz bulk, half-wavelength thin-film and quarter-wavelength thin-film and to estimate their ablation thresholds. Despite the adiabatic local density approximation used in calculating the exchange-correlation potential, the reflectance and the ablation threshold obtained from our method agree well with the previous theoretical and experimental results. The method can be applied to estimate the ablation thresholds for optical materials in general.

Journal Articles

Numerical pump-probe experiments of laser-excited silicon in nonequilibrium phase

Sato, Shunsuke*; Yabana, Kazuhiro; Shinohara, Yasushi*; Otobe, Tomohito; Bertsch, G. F.*

Physical Review B, 89(6), p.064304_1 - 064304_8, 2014/02

 Times Cited Count:47 Percentile:89.22(Materials Science, Multidisciplinary)

We calculate the dielectric response of crystalline silicon following irradiation by a high-intensity laser pulse, modeling the dynamics by the time-dependent Kohn-Sham equations in the presence of the laser field. As expected, the excited silicon shows features of an electron-hole plasma of nonequilibrium phase in its response, characterized by a negative divergence in the real part of the dielectric function at small frequencies. We also find that the imaginary part of the dielectric function can be negative, particularly for the parallel polarization of pump and probe fields.

Journal Articles

Measurement of the Md$$^{3+}$$/Md$$^{2+}$$ reduction potential studied with flow electrolytic chromatography

Toyoshima, Atsushi; Li, Z.*; Asai, Masato; Sato, Nozomi; Sato, Tetsuya; Kikuchi, Takahiro; Kaneya, Yusuke; Kitatsuji, Yoshihiro; Tsukada, Kazuaki; Nagame, Yuichiro; et al.

Inorganic Chemistry, 52(21), p.12311 - 12313, 2013/11

 Times Cited Count:5 Percentile:26.88(Chemistry, Inorganic & Nuclear)

The reduction behavior of mendelevium (Md) was studied using a flow electrolytic chromatography apparatus. By applying appropriate potentials on the chromatography column, the more stable Md$$^{3+}$$ is reduced to Md$$^{2+}$$. The reduction potential of the Md$$^{3+}$$ + e$$^{-}$$ $$rightarrow$$ Md$$^{2+}$$ couple was determined to be -0.16$$pm$$0.05 V vs. a normal hydrogen electrode.

Journal Articles

Improvement of numerical analytical model for temperature of primary biological shielding toward HTTR-LOFC test with VCS inactive

Takada, Shoji; Yanagi, Shunki; Iigaki, Kazuhiko; Shinohara, Masanori; Tochio, Daisuke; Shimazaki, Yosuke; Ono, Masato; Sawa, Kazuhiro

UTNL-R-0483, p.9_1 - 9_10, 2013/03

no abstracts in English

Journal Articles

First-principles calculation to explore mechanisms of coherent phonon generation

Shinohara, Yasushi*; Otobe, Tomohito; Iwata, Junichi*; Yabana, Kazuhiro*

Nihon Butsuri Gakkai-Shi, 67(10), p.685 - 689, 2012/10

Coherent phonon is the macroscopic coherent oscillation of atoms in a solid state generating under the ultrafast laser pulse which is shorter than the frequency of the phonon. Some physical processes for the coherent phonon have been proposed. We are studying the computational method describing the dynamics of the electron and atom employing the time-dependent density functional theory. Our computational results show the origine of the coherent phonon in Si quantitatively.

188 (Records 1-20 displayed on this page)