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Sakon, Atsushi*; Hashimoto, Kengo*; Sano, Tadafumi*; Nakajima, Kunihiro*; Kanda, Shun*; Goto, Masaki*; Fukaya, Yuji; Okita, Shoichiro; Fujimoto, Nozomu*; Takahashi, Yoshiyuki*
KURNS Progress Report 2021, P. 100, 2022/07
The R&D of reactor noise analysis to obtain HTGR nuclear characteristics have been performed with Kyoto University Critical Assembly (KUCA). In the last study, a neutron detector located about 55 cm away of fuel assembly measured the auto power spectral density. However, the prompt neutron decay constants obtained by this detector was different from that of other detectors. The objective of this study is experimental study of reactor noise analysis by the power spectrum method using neutron detector placed outside reactor core.
Komatsu, Yuya*; Shimizu, Ryota*; Sato, Ryuhei*; Wilde, M.*; Nishio, Kazunori*; Katase, Takayoshi*; Matsumura, Daiju; Saito, Hiroyuki*; Miyauchi, Masahiro*; Adelman, J. R.*; et al.
Chemistry of Materials, 34(8), p.3616 - 3623, 2022/04
Times Cited Count：9 Percentile：75.5(Chemistry, Physical)Ishitsuka, Etsuo; Mitsui, Wataru*; Yamamoto, Yudai*; Nakagawa, Kyoichi*; Ho, H. Q.; Ishii, Toshiaki; Hamamoto, Shimpei; Nagasumi, Satoru; Takamatsu, Kuniyoshi; Kenzhina, I.*; et al.
JAEA-Technology 2021-016, 16 Pages, 2021/09
JAEA-Technology-2021-016.pdf:1.8MB
As a summer holiday practical training 2020, the feasibility study for nuclear design of a nuclear battery using HTTR core was carried out, and the downsizing of reactor core were studied by the MVP-BURN. As a result, it is clear that a 1.6 m radius reactor core, containing 54 (18
3 layers) fuel blocks with 20% enrichment of 
U, and BeO neutron reflector, could operate continuously for 30 years with thermal power of 5 MW. Number of fuel blocks of this compact core is 36% of the HTTR core. As a next step, the further downsizing of core by changing materials of the fuel block will be studied.
Fujimoto, Nozomu*; Tada, Kenichi; Ho, H. Q.; Hamamoto, Shimpei; Nagasumi, Satoru; Ishitsuka, Etsuo
Annals of Nuclear Energy, 158, p.108270_1 - 108270_8, 2021/08
Times Cited Count：3 Percentile：45.99(Nuclear Science & Technology)Ishitsuka, Etsuo; Nakashima, Koki*; Nakagawa, Naoki*; Ho, H. Q.; Ishii, Toshiaki; Hamamoto, Shimpei; Takamatsu, Kuniyoshi; Kenzhina, I.*; Chikhray, Y.*; Matsuura, Hideaki*; et al.
JAEA-Technology 2020-008, 16 Pages, 2020/08
JAEA-Technology-2020-008.pdf:2.98MB
As a summer holiday practical training 2019, the feasibility study for nuclear design of a nuclear battery using HTTR core was carried out, and the U enrichment and burnable poison of the fuel, which enables continuous operation for 30 years with thermal power of 5 MW, were studied by the MVP-BURN. As a result, it is clear that a fuel with U enrichment of 12%, radius of burnable poison and natural boron concentration of 1.5 cm and 2wt% are required. As a next step, the downsizing of core will be studied.
Ishitsuka, Etsuo; Matsunaka, Kazuaki*; Ishida, Hiroki*; Ho, H. Q.; Ishii, Toshiaki; Hamamoto, Shimpei; Takamatsu, Kuniyoshi; Kenzhina, I.*; Chikhray, Y.*; Kondo, Atsushi*; et al.
JAEA-Technology 2019-008, 12 Pages, 2019/07
JAEA-Technology-2019-008.pdf:2.37MB
As a summer holiday practical training 2018, the feasibility study for nuclear design of a nuclear battery using HTTR core was carried out. As a result, it is become clear that the continuous operations for about 30 years at 2 MW, about 25 years at 3 MW, about 18 years at 4 MW, about 15 years at 5 MW are possible. As an image of thermal design, the image of the nuclear battery consisting a cooling system with natural convection and a power generation system with no moving equipment is proposed. Further feasibility study to confirm the feasibility of nuclear battery will be carried out in training of next fiscal year.
Pyeon, C. H.*; Fujimoto, Atsushi*; Sugawara, Takanori; Iwamoto, Hiroki; Nishihara, Kenji; Takahashi, Yoshiyuki*; Nakajima, Ken*; Tsujimoto, Kazufumi
Nuclear Science and Engineering, 185(3), p.460 - 472, 2017/03
Times Cited Count：11 Percentile：72.62(Nuclear Science & Technology)Sensitivity and uncertainty analyses of lead (Pb) isotope cross sections are conducted with the use of sample reactivity experiments at the Kyoto University Critical Assembly (KUCA). With the combined use of the SRAC2006 and MARBLE code systems, attempts are made to precisely examine the contributions of the reactions and energy regions of Pb isotope cross sections to reactivity based on the covariance data of JENDL-4.0. Moreover, the effect of decreasing uncertainty is discussed in terms of the accuracy of sample reactivity by applying the cross section adjustment method to the uncertainty analyses. From the results of the sensitivity and uncertainty analyses, the reliability of Pb isotope cross sections, such as the Pb isotope covariance data of JENDL-4.0, is compared with the JENDL-3.3, ENDF/B-VII.0, and JEFF-3.1 libraries.
Pyeon, C. H.*; Fujimoto, Atsushi*; Sugawara, Takanori; Yagi, Takahiro*; Iwamoto, Hiroki; Nishihara, Kenji; Takahashi, Yoshiyuki*; Nakajima, Ken*; Tsujimoto, Kazufumi
Journal of Nuclear Science and Technology, 53(4), p.602 - 612, 2016/04
Times Cited Count：21 Percentile：88.83(Nuclear Science & Technology)Sample reactivity experiments on the uncertainty analyses of Pb nuclear data are carried out by substituting Al plates for Pb ones at the Kyoto University Critical Assembly, as part of basic research on Pb-Bi for the coolant. Numerical simulations of sample reactivity experiments are performed with the Monte Carlo calculation code MCNP6.1 together with four nuclear data libraries JENDL-3.3, JENDL-4.0, ENDF/B-VII.0 and JEFF-3.1, to examine the accuracy of cross-section uncertainties of Pb isotopes by comparing measured and calculated sample reactivities. A library update from JENDL-3.3 to JENDL-4.0 is demonstrated by the fact that the difference between Pb isotopes of the two JENDL libraries is dominant in the comparative study, through the experimental analyses of sample reactivity by the MCNP approach. In addition, JENDL-4.0 reveals a slight difference from ENDF/B-VII.0 in all Pb isotopes and 
Al, and from JEFF-3.1 in 
U and Al.
Koshimizu, Masanori*; Iwamatsu, Kazuhiro*; Taguchi, Mitsumasa; Kurashima, Satoshi; Kimura, Atsushi; Yanagida, Takayuki*; Fujimoto, Yutaka*; Watanabe, Kenichi*; Asai, Keisuke*
Journal of Luminescence, 169(Part B), p.678 - 681, 2016/01
We analyzed the effects of linear energy transfer (LET) on the scintillation properties of a Li glass scintillator, GS20. The scintillation time profiles were measured by using pulsed ion beams having different LETs. The rise in the scintillation time profiles was faster for higher LET, whereas the decay part was not significantly different for largely different LETs. The LET effects in the rise was ascribed to the effects of excited states interaction during the energy transfer process from the host glass to the luminescent centers, Ce
ions. Supposing that the light yield decreases with LET, the fast rise at high LET was explained in terms of the competition between the energy transfer and the quenching due to the excited states interaction.
Tanimoto, Masataka; Taguchi, Taketoshi; Okada, Manabu; Hanawa, Yoshio; Tsuchiya, Kunihiko; Ikeda, Masayuki*; Fujimoto, Yoichi*; Kotov, V.*; Kenzhin, E.*; Kenzhin, Y.*
JAEA-Technology 2011-001, 39 Pages, 2011/03
JAEA-Technology-2011-001.pdf:4.15MB
It is important problem to recycle the irradiated beryllium from the points of effective use of resources, reduction of radioactive waste and nuclear nonproliferation. The recycling of the irradiated beryllium has been considered as the part of the development of Irradiation technology for JMTR refurbishment and restart. The ISTC regular project (K-1566) on recycling technology of irradiated beryllium has been carried out in the Institute of Atomic Energy (IAE), National Nuclear Center of Republic of Kazakhstan (NNC-RK). This paper is described on the transport procedure and transport results of the irradiated beryllium from Japan Atomic Energy Agency (JAEA) to IAE, NNC-RK under the ISTC project.
and 
cross sections of the 
C(
,
)
O reaction at 
1.2 MeV using pulsed beamsMakii, Hiroyuki; Ueda, Hitoshi*; Temma, Yasuyuki*; Nagai, Yasuki*; Shima, Tatsushi*; Fujimoto, Shinya*; Segawa, Mariko; Mishima, Kenji*; Nishiyama, Jun*; Igashira, Masayuki*
AIP Conference Proceedings 1269, p.283 - 288, 2010/10
Times Cited Count：0 Percentile：0.02(Astronomy & Astrophysics)The C(,)O reaction cross section plays an important role in stellar evolution at the stage of helium-burning. However, the cross section at low energy still has a large uncertainty mainly due to the poor determination of the ratio of cross section to one. Hence, we have installed new system to make a precise measurement of the cross section. In this experiment, we used the high efficiency anti-Compton NaI(Tl) spectrometers with a large S/N ratio, an intense pulsed beams, and the monitoring system of target thickness. With use of the system we succeeded in removing a background due to neutron and could clearly detect the -ray from the C(,)O reaction with high statistics. We determined the and cross section down to 
1.2 MeV, and thus obtained results are compared to recent theoretical calculations.
Co in the digestive glands of the common octopus, 
, in the East China SeaMorita, Takami*; Otosaka, Shigeyoshi; Fujimoto, Ken*; Nishiuchi, Ko*; Kimoto, Katsunori*; Yamada, Haruya*; Kasai, Hiromi*; Minakawa, Masayuki*; Yoshida, Katsuhiko*
Marine Pollution Bulletin, 60(8), p.1193 - 1199, 2010/08
Times Cited Count：3 Percentile：10.23(Environmental Sciences)Significant concentrations of Co, 
Cs and 
Ag were detected in common octopus specimens collected in the East China Sea during two periods, 1986-1989 and 1996-2005. The radionuclides detected in the former period were thought to originate from the global fallout. On the other hand, the source of Co in the latter period has remained unclear because the Co concentration decreased continuously with shorter half-lives than the physical half-lives. This tendency suggests that the source of Co in 1996-2005 was identical and was temporary supplied to the East China Sea. Investigations of common octopus in the other area indicated that the origin of the pollutant source of Co in 1996-2005 occurred locally in the restricted area in the East China Sea rather than in the coastal area of Japan.
Morita, Takami*; Niwa, Kentaro*; Fujimoto, Ken*; Kasai, Hiromi*; Yamada, Haruya*; Nishiuchi, Ko*; Sakamoto, Tatsuya*; Godo, Waichiro*; Taino, Seiya*; Hayashi, Yoshihiro*; et al.
Science of the Total Environment, 408(16), p.3443 - 3447, 2010/06
Times Cited Count：13 Percentile：33(Environmental Sciences)Iodine-131 (
I) was detected in brown algae collected off the Japanese coast. The maximum measured specific activity of I in brown algae was 0.37
0.010 Bq/kg-wet. Cesium-137 (Cs) was also detected in all brown algal samples used in this study. There was no correlation between specific activities of I and Cs in these seaweeds. Low specific activity and minimal variability of Cs in brown algae indicated that past nuclear weapon tests were the source of Cs. Although nuclear power facilities are known to be pollution sources of I, there was no relationship between the sites where I was detected and the locations of nuclear power facilities. Most of the sites where I was detected were near big cities with large populations. On the basis of the results, we suggest that the likely pollution source of I, detected in brown seaweeds, is not nuclear power facilities, but nuclear medicine procedures.
Tochio, Daisuke; Nojiri, Naoki; Hamamoto, Shimpei; Inoi, Hiroyuki; Sekita, Kenji; Kondo, Masaaki; Saikusa, Akio; Kameyama, Yasuhiko; Saito, Kenji; Fujimoto, Nozomu
JAEA-Technology 2009-005, 47 Pages, 2009/05
JAEA-Technology-2009-005.pdf:4.01MB
HTTR is now conducted in-service operation through the rise-to power operation with rated operation or high-temperature test operation from achievement of first criticality at 1998. In order to demonstrate to supply stable heat to heat utilization system for long-term, HTTR was conducted rated/parallel-loaded 30-days operation. This paper reports the characteristics of long-term operation for HTTR.
Nakano, Tomohide; Kubo, Hirotaka; Asakura, Nobuyuki; Takenaga, Hidenobu; Oyama, Naoyuki; Kawashima, Hisato; Fujimoto, Kayoko
Nuclear Fusion, 48(8), p.085002_1 - 085002_8, 2008/08
Times Cited Count：13 Percentile：46.66(Physics, Fluids & Plasmas)Particle control is one of the key issues for steady-state operation in fusion reactors. In short discharges, the first wall absorbs hydrogen particles and it works as a pump (wall pumping). The wall pumping is effective to control the plasma density. However, in future tokamak devices, wall retention increases in a long discharge. Then, it is expected that the wall retention is saturated and the wall pumping does not work. Therefore, for steady-state operation, particle control by active divertor pumping without the wall pumping should be established. In JT-60U, long-pulse high-density H-mode plasmas have been sustained by divertor pumping under global wall saturation. The energy confinement and ELM activity can be sustained, while wall pumping does not work and even outgas appears. The outgas is attributed to increase in the divertor-plate temperature. On the other hand, wall pumping continues for longer than 20 s in high-density (ne 0.8 nGW) discharges with an X-point MARFE and detached divertor plasma. X-point MARFEs have also been controlled by the divertor pumping. As a result, the electron density control by the divertor pumping and the gas puffing is effective under the wall saturation. However, it should be noted that the wall-pumping rate changes to maintain the electron density against the control. The change in the wall pumping suggests dynamic equilibrium between particle flux and desorption as an important wall-pumping mechanism.
Tokunaga, Yo; Sakai, Hironori; Fujimoto, Tatsuya; Kambe, Shinsaku; Walstedt, R. E.*; Ikushima, Kenji*; Yasuoka, Hiroshi; Aoki, Dai*; Homma, Yoshiya*; Haga, Yoshinori; et al.
Journal of Alloys and Compounds, 444-445, p.241 - 245, 2007/10
Times Cited Count：19 Percentile：68.81(Chemistry, Physical)In this paper, we present our recent NMR works on Neptunium and Plutonium compounds. In order to elucidate the nature of the exotic multipolar ordered phase of NpO
, we have initiated the first NMR measurements on this system. We have shown that direct observation of multipole order parameters is possible by means of NMR. Our NMR results provide further insight into the microscopic nature of multipole phase transitions in f-electron systems. We have also performed 
Ga NMR/NQR studies on a single crystal of PuRhGa
. From the temperature dependence of the spin-lattice relaxation rate (
), we have found that PuRhGa is an unconventional superconductor having an anisotropic superconducting (SC) gap 2
=5
. Furthermore, we have confirmed the Knight shift to be decreased below 
. This gives strong evidence for spin singlet SC pairing.
Kubo, Hirotaka; Nakano, Tomohide; Asakura, Nobuyuki; Takenaga, Hidenobu; Tsuzuki, Kazuhiro; Oyama, Naoyuki; Kawashima, Hisato; Shimizu, Katsuhiro; Urano, Hajime; Fujimoto, Kayoko; et al.
Proceedings of 21st IAEA Fusion Energy Conference (FEC 2006) (CD-ROM), 8 Pages, 2007/03
no abstracts in English
; Comparison with UO from 
O-NMRTokunaga, Yo; Homma, Yoshiya*; Kambe, Shinsaku; Aoki, Dai*; Ikushima, Kenji; Sakai, Hironori; Ikeda, Shugo; Yamamoto, Etsuji; Nakamura, Akio; Shiokawa, Yoshinobu; et al.
Journal of the Physical Society of Japan, 75(Suppl.), p.33 - 35, 2006/08
The low-temperature phase transition in NpO has attracted much attention as a promising candidate for a new class of phase transitions associated with octupolar degrees of freedom. In order to elucidate the nature of this exotic phase transition in NpO, we have initiated the first O-NMR measurements on this system using a powder sample. From the O-NMR spectrum, the occurrence of two inequivalent oxygen sites has been confirmed below 
= 26 K. It has also been shown that the temperature and field dependence of the O NMR spectrum can be understood by considering an unconventional hyperfine interaction between the O nuclear spins and field-induced antiferromagnetic moments arising from the longitudinal triple-
antiferro-quadrupolar order. These NMR results give strong evidence for the occurrence of the longitudinal triple- multipole structure in NpO. We will also discuss our recent O-NMR results in a single crystal.
Sato, Hitoshi*; Yoshikawa, Kunta*; Hiraoka, Koichi*; Arita, Masashi*; Fujimoto, Koji*; Kojima, Kenichi*; Muro, Takayuki*; Saito, Yuji; Sekiyama, Akira*; Suga, Shigemasa*; et al.
Physical Review B, 69(16), p.165101_1 - 165101_6, 2004/04
Times Cited Count：33 Percentile：77.9(Materials Science, Multidisciplinary)no abstracts in English
Nakagawa, Shigeaki; Fujimoto, Nozomu; Shimakawa, Satoshi; Nojiri, Naoki; Takeda, Takeshi; Saikusa, Akio; Ueta, Shohei; Kojima, Takao; Takada, Eiji*; Saito, Kenji; et al.
JAERI-Tech 2002-069, 87 Pages, 2002/08
JAERI-Tech-2002-069.pdf:10.12MB
Rise-to-power test in the HTTR has been performed from April 23rd to June 6th in 2000 as phase 1 test up to 10MW, from January 29th to March 1st in 2001 as phase 2 test up to 20MW in the rated operation mode and from April 14th to June 8th in 2001 as phase 3 test up to 20MW in the high temperature test operation mode. Phase 4 test to achieve the thermal reactor power of 30MW started from October 23rd in 2001. On December 7th it was confirmed that the thermal reactor power reached to 30MW and the reactor outlet coolant temperature reached to 850
C. JAERI obtained the certificate of pre-operation test from MEXT because all the pre-operation tests by MEXT were passed successfully. From the test results of rise-up-power test up to 30MW, the performance of reactor and cooling system were confirmed, and it was confirmed that an operation of reactor facility could be performed safely. Some problems to be solved were found through tests. By means of solving them, the reactor operation with the reactor outlet coolant temperature of 950C will be achievable.
