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Ma, B.*; Teshigawara, Makoto; Wakabayashi, Yasuo*; Yan, M.*; Hashiguchi, Takao*; Yamagata, Yutaka*; Wang, S.*; Ikeda, Yujiro*; Otake, Yoshie*
Nuclear Instruments and Methods in Physics Research A, 995, p.165079_1 - 165079_7, 2021/04
Times Cited Count:2 Percentile:34.88(Instruments & Instrumentation)We have optimized a cold neutron moderator to be operated at the RIKEN accelerator-driven compact neutron source. We selected a safe and easy to manage material, mesitylene, as the RANS cold moderator. An efficient moderator system was designed by studying and optimizing a coupled cold neutron moderator of mesitylene at 20 K with a polyethylene (PE) pre-moderator at room temperature in the slab geometry with Particle and Heavy Ion Transport code System (PHITS) simulations. The parameters of mesitylene and PE thickness, the reflector, and the shielding configuration were studied to increase cold neutron intensities. Consequently, an integrated cold neutron intensity of 1.1510n/cm/A at 2 m from the neutron-producing target was finally achieved, which was 12 times higher than that of the current PE moderator. The results showed attractive application prospect of mesitylene as cold neutron moderator material.
Kitazato, Kohei*; Milliken, R. E.*; Iwata, Takahiro*; Abe, Masanao*; Otake, Makiko*; Matsuura, Shuji*; Takagi, Yasuhiko*; Nakamura, Tomoki*; Hiroi, Takahiro*; Matsuoka, Moe*; et al.
Nature Astronomy (Internet), 5(3), p.246 - 250, 2021/03
Times Cited Count:43 Percentile:96.93(Astronomy & Astrophysics)Here we report observations of Ryugu's subsurface material by the Near-Infrared Spectrometer (NIRS3) on the Hayabusa2 spacecraft. Reflectance spectra of excavated material exhibit a hydroxyl (OH) absorption feature that is slightly stronger and peak-shifted compared with that observed for the surface, indicating that space weathering and/or radiative heating have caused subtle spectral changes in the uppermost surface. However, the strength and shape of the OH feature still suggests that the subsurface material experienced heating above 300 C, similar to the surface. In contrast, thermophysical modeling indicates that radiative heating does not increase the temperature above 200 C at the estimated excavation depth of 1 m, even if the semimajor axis is reduced to 0.344 au. This supports the hypothesis that primary thermal alteration occurred due to radiogenic and/or impact heating on Ryugu's parent body.
Pyon, S.*; Taen, Toshihiro*; Otake, Fumiaki*; Tsuchiya, Yuji*; Inoue, Hiroshi*; Akiyama, Hiroki*; Kajitani, Hideki; Koizumi, Norikiyo; Okayasu, Satoru; Tamegai, Tsuyoshi*
Applied Physics Express, 6(12), p.123101_1 - 123101_4, 2013/12
Times Cited Count:21 Percentile:63.34(Physics, Applied)We demonstrate a large enhancement of critical current density () up to 1.0 10 A/cm at 5 K under self-field in (Ba,K)FeAs single crystals by irradiating 320 MeV Au ions. With the very promising potential of this material in mind, we have fabricated a (Ba,K)FeAs superconducting wire through a powder-in-tube method combined with the hot isostatic pressing technique, whose effectiveness has been proven in industrial Bi2223 tapes. The Jc in the wire at 4.2 K has reached 37 kA/cm under self-field and 3.0 kA/cm at 90 kOe. Magneto-optical imaging of the wire confirmed the large intergranular Jc in the wire core.
Sato, Ikken; Tobita, Yoshiharu; Konishi, Kensuke; Kamiyama, Kenji; Toyooka, Junichi; Nakai, Ryodai; Kubo, Shigenobu*; Kotake, Shoji*; Koyama, Kazuya*; Vassiliev, Y. S.*; et al.
Journal of Nuclear Science and Technology, 48(4), p.556 - 566, 2011/03
In the JSFR design, elimination of severe recriticality events in the Core Disruptive Accident (CDA) is intended as an effective measure to assure retention of the core materials within the reactor vessel. The design strategy is to control the potential of excessive void reactivity insertion in the Initiating Phase selecting appropriate design parameters such as maximum void reactivity on one hand, and to exclude core-wide molten-fuel-pool formation, which has been the main issue of CDA, with introduction of Inner Duct on the other hand. The effectiveness of these measures are reviewed based on existing experimental data and evaluations performed with validated analysis tools. It is judged that the present JSFR design can exlude severe power burst events.
Konishi, Kensuke; Toyooka, Junichi; Kamiyama, Kenji; Sato, Ikken; Kubo, Shigenobu*; Kotake, Shoji*; Koyama, Kazuya*; Vurim, A. D.*; Gaidaichuk, V. A.*; Pakhnits, A. V.*; et al.
Nuclear Engineering and Design, 237(22), p.2165 - 2174, 2007/11
Times Cited Count:42 Percentile:92.58(Nuclear Science & Technology)The WF (Wall Failure) test of the EAGLE program, in which 2kg of uranium dioxide fuel-pins were melted by nuclear heating, was successfully conducted in the IGR of NNC/Kazakhstan. In this test, a 3mm-thick stainless steel (SS) wall structure was placed between fuel pins and a 10mm-thick sodium-filled channel (sodium gap). During the transient, fuel pins were heated, which led to the formation of a fuel-steel mixture pool. Under the transient nuclear heating condition, the SS wall was strongly heated by the molten pool, leading to wall failure. The time needed for fuel penetration into the sodium-filled gap was very short (less than 1 second after the pool formation). The result suggests that molten core materials formed in hypothetical LMFBR core disruptive accidents have a certain potential to destroy SS-wall boundaries early in the accident phase, thereby providing fuel escape paths from the core region. The early establishment of such fuel escape paths is regarded as a favorable characteristic in eliminating the possibility of severe re-criticality events.
Konishi, Kensuke; Kubo, Shigenobu*; Sato, Ikken; Koyama, Kazuya*; Toyooka, Junichi; Kamiyama, Kenji; Kotake, Shoji*; Vurim, A. D.*; Gaidaichuk, V. A.*; Pakhnits, A. V.*; et al.
Proceedings of 5th Korea-Japan Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS-5), p.465 - 471, 2006/11
no abstracts in English
Konishi, Kensuke; Toyooka, Junichi; Kamiyama, Kenji; Sato, Ikken; Kubo, Shigenobu*; Kotake, Shoji*; Koyama, Kazuya*; Vurim, A. D.*; Gaidaichuk, V. A.*; Pakhnits, A. V.*; et al.
Proceedings of Technical Meeting on Severe Accident and Accident Management (CD-ROM), 16 Pages, 2006/03
no abstracts in English
Yamamoto, Kazuyoshi; Kumada, Hiroaki; Torii, Yoshiya; Hori, Naohiko; Kishi, Toshiaki; Takada, Juntaro*; Otake, S.*
Proceedings of 9th International Symposium on Neutron Capture Therapy for Cancer, p.243 - 244, 2000/10
no abstracts in English
Konishi, Kensuke; Toyooka, Junichi; Kamiyama, Kenji; Sato, Ikken; Kubo, Shigenobu*; Kotake, Shoji*; Koyama, Kazuya*; Vurim, A. D.*; Pakhnits, A. V.*; Gaidaichuk, V. A.*; et al.
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no abstracts in English
Kamiyama, Kenji; Konishi, Kensuke; Sato, Ikken; Kubo, Shigenobu*; Kotake, Shoji*; Shimakawa, Yoshio*; Koyama, Kazuya*; Zuyev, V.*; Vassiliev, Y. S.*; Kolodeshnikov, A.*
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no abstracts in English
Toyooka, Junichi; Konishi, Kensuke; Kamiyama, Kenji; Sato, Ikken; Kubo, Shigenobu*; Kotake, Shoji*; Koyama, Kazuya*; Vurim, A. D.*; Pakhnits, A. V.*; Gaidaichuk, V. A.*; et al.
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no abstracts in English
Konishi, Kensuke; Toyooka, Junichi; Kamiyama, Kenji; Sato, Ikken; Kubo, Shigenobu*; Kotake, Shoji*; Koyama, Kazuya*; Vurim, A. D.*; Gaidaichuk, V. A.*; Pakhnits, A. V.*; et al.
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no abstracts in English
Konishi, Kensuke; Toyooka, Junichi; Kamiyama, Kenji; Sato, Ikken; Kubo, Shigenobu*; Kotake, Shoji*; Koyama, Kazuya*; Vurim, A. D.*; Pakhnits, A. V.*; Gaidaichuk, V. A.*; et al.
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The EAGLE experimental program is dedicated to show experimental evidences supporting a safety logic eliminating the recriticality issue in the core disruptive accidents (CDAs) of sodium-cooled fast breeder reactors. In order to confirm an inherent nature of early fuel escape from the core region, both in-pile (using IGR) and out-of-pile experiments have been performed in the program. This presentation shows the preliminary interpretation of the second integral experiment, in which fuel discharge through a duct-type escape path (initially filled with sodium) was investigated using about 8kg of molten fuel. Energy insertion in this second experiment was smaller than that in the first experiment. The duct-wall failure timing was a little delayed compared with that in the first experiment, and the fuel discharged through the duct intermittently.
Koyama, Kazuya*; Saruyama, Ichiro*; Konishi, Kensuke; Toyooka, Junichi; Kamiyama, Kenji; Sato, Ikken; Kubo, Shigenobu*; Kotake, Shoji*; Vurim, A. D.*; Pakhnits, A. V.*; et al.
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The EAGLE experimental program is dedicated to show experimental evidences supporting a safety logic eliminating the recriticality issue in the core disruptive accidents (CDAs) of sodium-cooled fast breeder reactors. Two kinds of neutron detectors (one was placed in the test section and another was placed around IGR driver core for power monitoring use) were analyzed to get prospect that the data include information of molten-fuel motion in the in-pile test.
Konishi, Kensuke; Kubo, Shigenobu*; Koyama, Kazuya*; Kamiyama, Kenji; Toyooka, Junichi; Sato, Ikken; Kotake, Shoji*; Vurim, A. D.*; Zuyev, V.*; Pakhnits, A. V.*; et al.
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In the EAGLE program, several in-pile and out-of-pile tests have been conducted by August 2006, under a co-operation between JAEA and NNC/RK. The main objectives of these tests are; (1) to demonstrate effectiveness of special design concepts to eliminate the re-criticality issue in the course of CDAs of SFRs, and (2) to acquire basic information on early-phase relocation of molten-core materials toward cold regions surrounding the core, which would be applicable to various core design concepts. As the final step of this program, integral in-pile tests simulating realistic accident conditions were conducted. Geometry of the test apparatus adopted in these tests is corresponding to a typical special design concept equipped with a "discharge duct" within each fuel sub-assembly. In these tests, fuel-steel mixture pool was successfully realized and discharge of the pool materials through the duct was observed.
Toyooka, Junichi; Konishi, Kensuke; Kamiyama, Kenji; Sato, Ikken; Kubo, Shigenobu*; Kotake, Shoji*; Koyama, Kazuya*; Vurim, A. D.*; Pakhnits, A. V.*; Gaidaichuk, V. A.*; et al.
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no abstracts in English
Kubo, Shigenobu; Tobita, Yoshiharu; Sato, Ikken; Kotake, Shoji*; Endo, Hiroshi*; Koyama, Kazuya*; Konishi, Kensuke; Kamiyama, Kenji; Matsuba, Kenichi; Toyooka, Junichi; et al.
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As the results of good collaboration between Kazakhstan and Japan in EAGLE-1and 2, it was shown that there exists a solution to the recriticality issue of SFR, which has been one of the major safety issues for more than a half century from the beginning of the SFR development. Experimental techniques and facilities have been developed for the SFR severe accident study. Since 2014, JAEA participates the ASTRID program in which severe accident study is one of important issues. The EAGLE-1 and 2 data will be also used as an essential part of the severe accident study for ASTRID. EAGLE-3 was just started from beginning of 2015. Points of experiments moved into the later phase of core damage process, i.e., material relocation and cooling after achieving neutronic shutdown. A number of out-of-pile tests and in-pile tests are planned in coming five years.
Xu, P. G.; Iwamoto, Chihiro*; Takamura, Masato*; Otake, Yoshie*; Kurihara, Ryo*; Ueno, Kota*; Kataoka, Minami*; Yamamoto, Kazuyoshi; Harjo, S.; Shobu, Takahisa
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Xu, P. G.; Yamamoto, Kazuyoshi; Harjo, S.; Shobu, Takahisa; Iwamoto, Chihiro*; Takamura, Masato*; Otake, Yoshie*; Onuki, Yusuke*; Sato, Shigeo*; Liss, K.-D.*
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Xu, P. G.; Iwamoto, Chihiro*; Yamamoto, Kazuyoshi; Morooka, Satoshi; Takamura, Masato*; Wu, S.*; Otake, Yoshie*; Shobu, Takahisa
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