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Omori, Takazumi; Fuyushima, Takumi; Sayato, Natsuki; Saito, Nagatsuki; Takabe, Yugo; Endo, Yasuichi; Inoue, Shuichi; Wojtania, G.*; Migdal, M.*; Takeuchi, Tomoaki; et al.
JAEA-Technology 2026-006, 47 Pages, 2026/06
JAEA-Technology-2026-006.pdf:3.01MB
Japan Materials Testing Reactor (JMTR), which served as the core facility for neutron irradiation research including materials research and radioisotope production, has been decommissioned. As a result, it has become difficult to continue conducting irradiation tests domestically, as well as to transfer the operational expertise and irradiation technologies associated with test reactors, to address these challenges, it was decided to initiate JMTR alternative irradiation, in which foreign irradiation reactors are utilized to partially substitute for JMTR's irradiation capabilities. As a first step, based on the "Arrangement between the National Centre for Nuclear Research and the Japan Atomic Energy Agency for Cooperation in Research and Development on Testing Reactor". The MARIA reactor (30 MW) owned by the National Centre for Nuclear Research (NCBJ) was selected as the neutron irradiation facility, a temperature control system, which is one of JMTR's irradiation technologies, was introduced into the MARIA reactor, and irradiation tests were conducted. The results of this irradiation test confirmed that the combination of the newly introduced temperature control device and the JMTR irradiation test system operates without issues even after an irradiation period exceeding 150 days, it was also demonstrated that the tests could be conducted while continuously measuring the thermocouple temperature inside the capsule during irradiation, as well as the output of the LVDT and SPGD. Furthermore, regarding the constant temperature control of the irradiation capsule at 300
C constant temperature control test, which is highly demanded in materials irradiation testing, was conducted, during reactor power increases, when temperature fluctuations become significant, temperature control was maintained within 
6.3C, while during power decreases, it was controlled within 26.0C. These results indicate that irradiation testing with irradiation temperature control system developed by JMTR, can also be performed in the MARIA reactor, it was confirmed that it can be offered as an alternative irradiation field.
Hagiwara, Hiroki; Kosuge, Atsushi; Saito, Junichi; Namie, Masanari; Kisohara, Naoyuki; Minehara, Eisuke*; Tsuboi, Akihiko; Ishimori, Yuu
Next Research (Internet), 8, p.101581_1 - 101581_9, 2026/06
-iron at high pressures determined using 
neutron diffractionAoki, Katsutoshi*; Takano, Masahiro*; Fukuyama, Ko*; Kagi, Hiroyuki*; Machida, Akihiko*; Saito, Hiroyuki*; Hattori, Takanori; Sano, Asami; Funakoshi, Kenichi*
Physical Review B, 113(18), p.184440_1 - 184440_6, 2026/05
Times Cited Count：1The temperature dependence of the magnetic moment of bcc -iron was investigated over the range 300-950 K at pressures of approximately 2 and 6 GPa by neutron powder diffraction. The 
Fe isotope, whose neutron scattering length is approximately half that of naturally abundant Fe, was employed to enhance the relative contribution of magnetic scattering. Curie temperatures (
) were determined to be 946(30) K, 838(50) K and 740(40) K at 2.1, 6.0 and 6.7 GPa, respectively, defining a magnetic phase boundary described by (K) = 1043 - 49(7)
+ 1.3(1.2)
. Upon heating at 6.7 GPa, the 
structural transition was observed to follow the magnetic transition. This transition sequence indicates that the magnetic phase boundary lies on the low-temperature side of the phase boundary. Accordingly, the transition corresponds to a structural transformation from paramagnetic bcc to paramagnetic fcc iron.
As studied by X-ray magnetic circular dichroismWan, Y.*; Shibata, Goro; Takeda, Yukiharu*; Okane, Tetsuo; Saito, Yuji; Yamagami, Hiroshi; Fujimori, Atsushi*; 10 of others*
Physical Review Materials (Internet), 10(5), p.054402_1 - 054402_8, 2026/05
Times Cited Count：0Umeda, Maki; Chudo, Hiroyuki; Imai, Masaki; Matsuo, Mamoru; Sato, Nana; Mori, Michiyasu; Maekawa, Sadamichi*; Saito, Eiji
Applied Physics Letters, 128(12), p.122402_1 - 122402_6, 2026/03
Times Cited Count：0 Percentile：0.00(Physics, Applied)Kim, M.; Yoshimura, Kazuya; Sakuma, Kazuyuki; Malins, A.*; Abe, Tomohisa; Nakama, Shigeo; Machida, Masahiko; Saito, Kimiaki
Journal of Environmental Radioactivity, 294, p.107931_1 - 107931_8, 2026/03
Times Cited Count：0 Percentile：0.00(Environmental Sciences)This study quantitatively evaluated the effects of non-decontamination human activities, such as traffic, on ambient dose rates in residential areas near the Fukushima Daiichi Nuclear Power Plant through field measurements and simulations. Field surveys showed that areas with higher traffic had greater reductions in 
Cs deposition, suggesting that vehicular movement may enhance cesium weathering. Monte Carlo simulations using 3D-ADRES confirmed that human activities accelerate the decrease in ambient dose rates on paved surfaces, with reductions of up to approximately 50%. These results indicate that non-decontamination human activities significantly contribute to lowering ambient dose rates.
Saito, Yoshika*; Ito, Naomi*; Abe, Toshiki*; Yamamoto, Chika*; Matsumoto, Chihiro*; Zhao, T.*; Moriyama, Nobuaki*; Yoshimura, Kazuya; Sanada, Yukihisa; Tsubokura, Masaharu*
Journal of Radiological Protection, 46(1), p.013502_1 - 013502_8, 2026/03
Times Cited Count：0 Percentile：0.00(Environmental Sciences)
reactions on neutron-rich nuclei; Collectivity and resonances in low-energy cross sectionsSaito, Teruyuki; Matsuo, Masayuki*
Physical Review C, 113(3), p.034607_1 - 034607_16, 2026/03
Times Cited Count：0 Percentile：0.00(Physics, Nuclear)Cho, K.*; Yamashita, Kippei*; Kakutani, Shinnosuke*; Saito, Takuma*; Sasaki, Taisuke*; Sawaizumi, Katsuhiko*; Okugawa, Masayuki*; Koizumi, Yuichiro*; Mayama, Tsuyoshi*; Kikukawa, Taichi*; et al.
Acta Materialia, 303, p.121696_1 - 121696_18, 2026/01
Times Cited Count：6 Percentile：83.48(Materials Science, Multidisciplinary)Nagasumi, Satoru; Hasegawa, Toshinari; Iigaki, Kazuhiko; Nakagawa, Shigeaki; Kubo, Shinji; Shimazaki, Yosuke; Nakajima, Kunihiro; Sakurai, Yosuke; Shinohara, Masanori; Saito, Kenji; et al.
Nuclear Engineering and Design, 446(Part A), p.114542_1 - 114542_14, 2026/01
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)To demonstrate HTGR's safety features, a loss-of-forced-cooling (LOFC) test was conducted using the HTTR. In this test, the forced cooling in the reactor core was intentionally lost by shutting down all helium gas circulators (HGCs) without reactor scram. During steady-state operation at 100% reactor power (30 MW), after the LOFC, the reactor power spontaneously decreased. This power reduction occurred due to the negative reactivity feedback effect triggered by an increase in core temperature. The power stabilized at a lower value of 1.2% after re-criticality. Additionally, the measured radioactivity concentration in the primary coolant remained nearly unchanged during this LOFC operation and during an immediately subsequent HTTR operation. This indicates no failure of the coated particle fuel, even after the increase in core temperature associated with the LOFC event. These results provide experimental evidence of the safety features of HTGRs.
Makiuchi, Takahiko*; Kikkawa, Takashi; Imai, Masaki; Chudo, Hiroyuki; Saito, Eiji; 3 of others*
Physical Review Research (Internet), 7(3), p.033083_1 - 033083_7, 2025/09
Sato, Junya; Takahashi, Yuta; Sunahara, Jun*; Saito, Toshimitsu*; Yoshida, Yukihiko; Sone, Tomoyuki; Osugi, Takeshi
Progress in Nuclear Science and Technology (Internet), 8, p.307 - 312, 2025/09
/KNbO nanocomposite particlesYoneda, Yasuhiro; Kobayashi, Toru; Tsuji, Takuya; Shibata, Goro; Takeda, Yukiharu*; Saito, Yuji; Khanal, G. P.*; Fujii, Ichiro*; Ueno, Shintaro*; Sato, Yukio*; et al.
Japanese Journal of Applied Physics, 64(8), p.08SP07_1 - 08SP07_8, 2025/08
Times Cited Count：1 Percentile：36.38(Physics, Applied)It has become possible to synthesize high-quality composite nanoparticles in which a different material is grown on the surface of nanoparticle crystals. To evaluate such nanostructures, it is effective to combine different evaluation methods at various scales. We performed various structural and electronic state evaluations of BaTiO/KNbO nanocomposite particles using synchrotron radiation. From the structural evaluation, it was confirmed that the nanocomposite particles have a core of 100 nm of BaTiO covered with 20 nm of KNbO. The O-K absorption edge spectrum of the outermost surface KNbO was different from that of the bulk and nanoparticles, and it was found that the chemical bonding state changes when KNbO
is made into composite particles.
Nagasumi, Satoru; Hasegawa, Toshinari; Nakagawa, Shigeaki; Kubo, Shinji; Iigaki, Kazuhiko; Shinohara, Masanori; Saikusa, Akio; Nojiri, Naoki; Saito, Kenji; Furusawa, Takayuki; et al.
JAEA-Research 2025-005, 23 Pages, 2025/07
JAEA-Research-2025-005.pdf:2.68MB
A safety demonstration test under abnormal operating conditions using the HTTR (High Temperature Engineering Test Reactor) was conducted to demonstrate safety features of the HTGRs (High Temperature Gas-cooled Reactors). Under a simulation of a control rod shutdown failure, all primary helium gas circulators were intentionally stopped during a steady-state operation at 100% reactor thermal power (30 MW), temporal changes of the reactor power and temperatures around the reactor pressure vessel (RPV) were obtained after the complete loss of forced heat removal from the reactor core. After the event (primary coolant flow stopped), the reactor power quickly decreased due to the negative reactivity feedback associated with the core temperature rise, and then the reactor power spontaneously shifted to a stable state of low power (about 1.2%) even after a recriticality. Heat dissipation from RPV surface to a surrounding vessel cooling system (water-cooled panels) ensured the amount of heat removal required to maintain the reactor temperature constant in the low power state. In this way, the transition from the event occurrence to the stable and safety state, i.e., inherent safety features of HTGRs, were demonstrated in the case of core forced cooling loss without active shutdown operations.
Mei, H.; Aoyagi, Noboru; Saito, Takumi*; Tanaka, Kazuya; Sugiura, Yuki; Tachi, Yukio
Applied Clay Science, 276, p.107944_1 - 107944_8, 2025/07
Times Cited Count：3 Percentile：69.76(Chemistry, Physical)Hirooka, Shun; Vauchy, R.; Horii, Yuta; Sunaoshi, Takeo*; Saito, Kosuke; Ozawa, Takayuki
Proceedings of Workshop on Fuel Performance Assessment and Behaviour for Liquid Metal Cooled Fast Reactors (Internet), 8 Pages, 2025/07
no abstracts in English
Machida, Akihiko*; Saito, Hiroyuki*; Aoki, Katsutoshi*; Komatsu, Kazuki*; Hattori, Takanori; Sano, Asami; Funakoshi, Kenichi*; Machida, Shinichi*; Sato, Toyoto*; Orimo, Shinichi*
Physical Review B, 111(22), p.224413_1 - 224413_6, 2025/06
Times Cited Count：1 Percentile：36.38(Materials Science, Multidisciplinary)The crystal and magnetic structures of antiferromagnetic Mn deuterides formed by hydrogenating Mn metal at high temperature and high pressure, fcc 
-MnDx and hcp 
-MnDx, were investigated by in-situ neutron powder diffraction. Deuterium atoms partially occupied the octahedral interstitial positions of the fcc and hcp metal lattices. The site occupancies increased rapidly with decreasing temperature from 
700 to 450 K and remained down to 300 K. N
el temperature of 543(10) K was determined for -MnD
. For -MnD
, saturation magnetic moment and Nel temperature were determined to be 0.82(1) 
and 347(3) K, respectively. The Nel temperatures determined for -MnD and -MnD are consistent with those predicted by the respective Slater-Pauling curves proposed in previous studies. The updated Nel temperatures provide insights into the development of more accurate Slater-Pauling curves based on electronic band structure calculations.
Chiu, I.-H.; Osawa, Takahito; Ninomiya, Kazuhiko*; Takeda, Shinichiro*; Takahashi, Tadayuki*; Katsuragawa, Miho*; Watanabe, Shin*; Kubo, Kenya*; Saito, Tsutomu*; Mizumoto, Kazumi*; et al.
npj Heritage Science (Internet), 13, p.154_1 - 154_9, 2025/05
Times Cited Count：1 Percentile：82.33(Humanities, Multidisciplinary)Kato, Masaru*; Zheng, J.*; Deng, Y.*; Saito, Fumie*; Unuma, Yuki*; Oka, Sayuki*; Tamura, Kazuhisa; Yagi, Ichizo*
ACS Catalysis, 15(10), p.7710 - 7719, 2025/04
Times Cited Count：4 Percentile：60.79(Chemistry, Physical)Chudo, Hiroyuki; Yokoi, Naoto*; Matsuo, Mamoru; Harii, Kazuya*; Suzuki, Jun*; Imai, Masaki; Sato, Masahiro*; Maekawa, Sadamichi*; Saito, Eiji*
Physical Review Letters, 134(13), p.130603_1 - 130603_5, 2025/04
Times Cited Count：1 Percentile：44.91(Physics, Multidisciplinary)