Toshiaki MANAKA,^1)* Goroh ITOH,²⁾ Junya KOBAYASHI,²⁾ Shigeru KURAMOTO²⁾ and Yuji HATANO³⁾

1) Department of Environmental Materials Engineering, NationalInstitute of Technology (KOSEN), Niihama College
2) Major in Mechanical Systems Engineering, Graduate School of Science and Engineering, Ibaraki University
3) Hydrogen Isotope Center, Organization for Promotion of Research, University of Toyama

Abstract
To understand the process and mechanism for hydrogen embrittlement in steels, visualization of the location of hydrogen is essential. In the present study, two visualization techniques, hydrogen microprint technique (HMT) and tritium autoradiography (TAR), were applied to a pure iron sheet 20% tensile-deformed with cathodic hydrogen charging. When the specimen was covered with photographic emulsion shortly (40 min) after the deformation, HMT showed that the charged hydrogen atoms diffused out at majorly grain boundaries and minorly in the grain interiors. The TAR, conducted on the same sample but completely de-hydrogenated and then charged with tritium, revealed that hydrogen enhances the formation of vacancies or vacancy clusters with plastic deformation, which are located along grain boundaries and deformation bands and act as relatively stable trapping sites for tritium.

https://doi.org/10.2355/isijinternational.ISIJINT-2023-279
Accepted:October 26, 2023

M. Yajima², M. Tokitani², Y. Oya⁵, S.E. Lee⁶, Y. Hatano⁶, N. Asakura⁷, T. Hayashi⁸,M. Oyaidzu⁸, J. Likonen⁹, A. Widdowson¹⁰, M. Rubel^11,12 and JET Contributors

1 Ibaraki University Graduate School of Science and Engineering, Mito, Japan
2 National Institute for Fusion Science, Toki, Japan
3 Kindai University, Higashi-Osaka, Japan
4 SOKENDAI, Toki, Japan
5 Shizuoka University, Shizuoka, Japan
6 Hydrogen Isotope Research Center, University of Toyama, Toyama, Japan
7 National Institute for Quantum and Radiological Science and Technology, Naka, Japan
8 National Institute for Quantum and Radiological Science and Technology, Rokkasho, Japan
9 VTT Technical Research Centre of Finland, Otakaari 3J, 02150 Espoo, Finland
10 Culham Centre for Fusion Energy, United Kingdom Atomic Energy Authority, Culham Science Center, Abingdon OX14 3DB, United Kingdom of Great Britain and Northern Ireland
11 KTH Royal Institute of Technology, 100 44 Stockholm, Sweden
12 Uppsala University, Box 516, 751 20 Uppsala, Sweden

Abstract
Divertor tiles after Joint European Torus-ITER like wall (JET-ILW) campaigns and dust collected after JET-C and JET-ILW operation were examined by a set of complementary techniques (full combustion and radiography) to determine the total, specific and areal tritium activities, poloidal tritium distribution in the divertor and the presence of that isotope in individual dust particles. In the divertor tiles, the majority of tritium is detected in the surface region and, the areal activities in the ILW divertor are in the 0.5–12 kBq cm⁻² range. The activity in the ILW dust is associated mainly with the presence of carbon particles being a legacy from the JET-C operation. The total tritium activities show significant differences between the JET operation with ILW and the earlier phase with the carbon wall (JET-C) indicating that tritium retention has been significantly decreased in the operation with ILW.

https://doi.org/10.1088/1741-4326/ad0c08
Accepted:13 November 2023

M. Hatakeyama ^a, Y. Asai ^b, D. Nakato ^b, M. Nishimura ^b, Y. Hatano ^c, S. Sunada ^a K. Sato ^d

a Graduate School of Science and Engineering for Research, University of Toyama
b Graduate School of Science and Engineering for Education, University of Toyama
c Hydrogen Isotope Research Center, University of Toyama
d Graduate School of Science and Engineering, Kagoshima University

Abstract
Precipitation-hardened Cu–Cr–Zr alloy is proposed as a heat sink material for various components of the ITER owing to its high strength, high conductivity, and superior resistance against neutron irradiation. Oxidedispersion- strengthened copper (ODS-Cu) was selected as the candidate material. Hydrogen embrittlement of Cu–Cr–Zr, Cu–Cr, and ODS-Cu (GlidCop® CuAl60) alloys was evaluated using the slow strain rate technique (SSRT) in 0.1 M sodium sulfate (Na₂SO₄) solutions under cathodic hydrogen charging or after D₂ gas exposure. Thermal desorption spectroscopy (TDS) measurements were performed to estimate the differences in the hydrogen-trapping sites using hydrogen charging methods. According to the TDS results, the quantity of hydrogen retained in ODS-Cu exceeded that in the other alloys by an order of magnitude because of hydrogen trapping at the grain boundaries and the particle/matrix interface. Cu–Cr–Zr alloys tend to trap more hydrogen than Cu–Cr alloys because of the addition of Zr. As a result of the SSRT, no hydrogen embrittlement was observed in any alloy, regardless of the hydrogen charging method. All alloys exhibited excellent hydrogen embrittlement resistance under the conditions adopted in this study.

https://doi.org/10.1016/j.nme.2024.101580
Accepted:3 January 2024

山ノ井航平，岩本晃史^{1 ）}，原　正憲^{2 ）}
YAMANOI Kohei, IWAMOTO Akifumi^{1 ）} and HARA Masanori ^{2 ）}
大阪大学レーザー科学研究所，^{1 ）}核融合科学研究所，^{2 ）}富山大学研究推進機構水素同位体科学研究センター

Abstract
    重水素-トリチウムを燃料とする核融合炉の設計においては，主な燃料の投入方法である極低温で固体のDT混合ペレットの作成手法および検査手法の確立が重要である．一方でトリチウムは標準状態で気体状の放射性物質であり，材料への高い透過性という取り扱いの難しさから取り扱いできる施設が限られており，基礎的なデータが不足している．このため，我々は重水素-トリチウムを固化し，光学的検査に必須である屈折率を測定した．水素同位体は固化点が異なるため，固化過程において同位体分離が生じる可能性がある．屈折率を用いて，この同位体分離を測定した．この手法は，実際のDT 混合ペレットの検査手法へと応用が可能である．

Keywords: deterium-tritium pellet, fusion, solid tritium, inspection method, optical measurement, fuel pellet
Accepted:2023年11月21日

M.I. Kobayashi^1,2, S. Yoshihashi³, K. Ogawa^1,2, M. Isobe^1,2, T. Aso⁴, M. Hara⁵,S. Sangaroon⁶, S. Tamaki⁷, I. Murata⁷, S. Toyama⁸, M. Miwa⁸, S. Matsuyama⁸ and M. Osakabe^1,2

1 National Institute for Fusion Science, Toki, Japan
2 The Graduate University for Advanced Studies, SOKENDAI, Toki, Japan
3 Nagoya University, Nagoya, Aichi, Japan
4 National Institute of Technology, Toyama College, Toyama, Toyama, Japan
5 University of Toyama, Toyama, Toyama, Japan
6 Mahasarakham University, Maha Sarakham, Thailand
7 Osaka University, Suita, Osaka, Japan
8 Tohoku University, Sendai, Miyagi, Japan

Abstract
This paper presents the development of a simultaneous measurement method for fast neutron energy spectra and tritium production rates within mixed radiation fields using a single crystal chemical vapour deposition diamond detector combined with a lithium fluoride (LiF) foil. The method involves the separation of pulses with rectangular shapes and the determination of the depth position within the single crystal diamond (SCD) struck by fast neutrons or nuclear reaction products including recoil tritons from the LiF foil based on pulse width, extracting pulse events occurred at the specific bulk region and the surface region of the SCD. Subsequently, unfolding techniques were employed to analyse the energy deposition spectrum of pulses at the specific bulk region which are induced only by fast neutrons, allowing the deduction of the fast neutron energy spectrum. To evaluate the tritium production rate, the energy deposition spectrum of pulses from events occurring at the SCD surface facing the LiF foil was analysed. By estimating the energy deposition spectrum solely induced by fast neutrons striking the SCD surface and subtracting it from the energy deposition spectrum of events at the SCD surface, the contribution of energetic ions, such as recoil tritons generated by the ⁶Li(n,α)³H reaction in the LiF foil, was determined. The fast neutron flux and tritium.

https://doi.org/10.1088/1741-4326/ad3f2e
Accepted:16 April 2024

Jiaqi Zhang, ^a Akifumi Iwamoto,^a,b Keisuke Shigemori,^a Masanori Hara,^c and Kohei Yamanoi^a

a Osaka University, Institute of Laser Engineering, Osaka 565-0871, Japan
b National Institutes of Natural Sciences, National Institute for Fusion Science, Gifu, Japan
c University of Toyama, Academic Assembly, Toyama, Japan

Abstract
Fuel pellets made of a solid deuterium-tritium (D-T) mixture are supplied for inertial confinement fusion. Characterization of the D-T mixture is fundamental for the design and production of high-quality fuel pellets. However, during the phase transition, isotopologue fractionation may lead to fractional crystallization in the solid phase of the hydrogen isotopologue mixture. If this phenomenon occurs in solid D-T fuel, it will reduce the reaction efficiency of nuclear fusion. Currently, there is no effective observation method for fractional crystallization. This study aims to quantify the degree of fractional crystallization of the hydrogen isotopologues mixture in the solid phase using the refractive index measurement. For this method, refractive index information on the hydrogen isotopologues is necessary, therefore the temperature and wavelength dependences of the refractive index of hydrogen isotopologues need to be measured. Then, using the refractive index distribution of the solid D-T will show the composition distribution of isotopologues for assessing the fractional crystallization. Particularly, as far as we know, this is the first time that the measured values of the refractive index versus wavelength of solid D₂ have been obtained. Understanding the wavelength dependence of the refractive index for the dispersion compensation allows for a wider application of the fractionated crystallographic observation method.

DOI: https://doi.org/10.1080/15361055.2023.2197810
Accepted for Publication March 27, 2023

Baowang Lu ^a, Yuyu Liu ^b, Mitsuhiro Inoue ^c, Eric Rukundo ^b, Takayuki Abe ^c

a National Institute of Clean-and-Low-Carbon Energy, Future Science City, Changping District, Beijing 102211, China
b Institute for Sustainable Energy, College of Sciences, Shanghai University, Shanghai 200444, China
c Hydrogen Isotope Research Center, Organization for Promotion of Research, University of Toyama, Gofuku 3190, Toyama 930-8555, Japan

Abstract
The study of carbon dioxide (CO₂) methanation mechanisms widely argues on the nature and formation of intermediates. How reactants dissociate is still poorly understood. To gain deeper knowledge on its mechanism, we focused on studying reactants dissociation. After H₂ dissociation and diffusion, the spillover H atom was observed, as well as the confirmation of H cluster formation on metal through aggregation by simulation and experiment. This H cluster facilitated C-O bond scission to easily form H ligand cobonded to metal, and thus resulted in high CO₂ methanation performance. Four driving forces could dissociate CO₂, three of them came from supports and metals, and another one was atomic H on metal as the strongest force. This simple and convenient method has wide adaptability and can be developed as an effective standard method for studying CO₂ dissociation. The facile dissociation study of reactants would be very helpful in understanding the CO₂ hydrogenation mechanism.

https://doi.org/10.1016/j.cej.2024.152021
Accepted:6 May 2024

Akira Taguchi, * Haruka Hamashima, Takumi Nakamori, and Yuki Yoneyama
University of Toyama, Hydrogen Isotope Research Center

Abstract
We examine the hydrogen adsorption behavior of chabazite (CHA) and Linde Type A (LTA) zeolites, both of which possess an eight-membered ring (Si₈O₈), as the temperature was increased from 77 K (thermal adsorption spectroscopy). The CHA-type zeolites started to uptake hydrogen at around 200 K, whereas no other adsorbent showed any hydrogen uptake. The hydrogen adsorption temperature of CHA was similar to that observed by thermal desorption spectroscopy. A high D₂/H₂ separation ability at relatively high temperature in the CHA-type zeolites may be expected in the intrinsic adsorption property.

https://doi.org/10.1080/15361055.2023.2194239
Accepted:March 13, 2023

Jiaqi Zhang, ^a* Akifumi Iwamoto,^a,b Keisuke Shigemori,^a Masanori Hara,^c and Kohei Yamanoi^a

a Osaka University, Institute of Laser Engineering
b National Institutes of Natural Sciences, National Institute for Fusion Science
c University of Toyama, Academic Assembly

Abstract
Fuel pellets made of a solid deuterium-tritium (D-T) mixture are supplied for inertial confinement fusion. Characterization of the D-T mixture is fundamental for the design and production of high-quality fuel pellets. However, during the phase transition, isotopologue fractionation may lead to fractional crystallization in the solid phase of the hydrogen isotopologue mixture. If this phenomenon occurs in solid D-T fuel, it will reduce the reaction efficiency of nuclear fusion. Currently, there is no effective observation method for fractional crystallization. This study aims to quantify the degree of fractional crystallization of the hydrogen isotopologues mixture in the solid phase using the refractive index measurement. For this method, refractive index information on the hydrogen isotopologues is necessary, therefore the temperature and wavelength dependences of the refractive index of hydrogen isotopologues need to be measured. Then, using the refractive index distribution of the solid D-T will show the composition distribution of isotopologues for assessing the fractional crystallization. Particularly, as far as we know, this is the first time that the measured values of the refractive index versus wavelength of solid D2 have been obtained. Understanding the wavelength dependence of the refractive index for the dispersion compensation allows for a wider application of the fractionated crystallographic observation method.

https://doi.org/10.1080/15361055.2023.2197810
Accepted:March 27, 2023

Kazuyuki Shimizu ^a, Katsuhiko Nishimur^{a b}, Kenji Matsuda ^b, Satoshi Akamaru ^b,Norio Nunomura ^b, Takahiro Namiki ^b, Taiki Tsuchiy^{a b}, Seungwon Lee ^b, Wataru Higemoto ^c,d,Tomohito Tsuru ^e, Hiroyuki Toda ^f

a Department of Physical Science and Materials Engineering, Iwate University
b Graduate School of Science and Engineering, University of Toyama
c Advanced Science Research Center, Japan Atomic Energy Agency, Tokai
d Department of Physics, Tokyo Institute of Technology, Meguro
e Nuclear Science and Engineering Center, Japan Atomic Energy Agency
f Department of Mechanical Engineering, Kyushu University, Fukuoka

Abstract
Hydrogen at the mass ppm level causes hydrogen embrittlement in metallic materials, but experimentally elucidating the hydrogen trapping sites is extremely difficult. We exploit the fact that positive muons can act as light isotopes of hydrogen to study the trapping state of hydrogen in matter. Zero-field muon spin relaxation experiments and density functional theory (DFT) calculations of the hydrogen trapping energy are carried out for Al₆Mn. The DFT calculations reveal four possible trapping sites for hydrogen in Al6Mn, at which the hydrogen trapping energies are 0.168 (site 1), 0.312 (site 2), 0.364 (site 3), and 0.495 (site 4) in units of eV/atom. The variations in the deduced dipole field width (Δ) with temperature indicate noticeable changes at 94, 193, and 236 K. Considering the site densities, the observed Δ change temperatures are interpreted as muon trapping at sites 1, 3, and 4.

https://doi.org/10.1016/j.scriptamat.2024.116051
Accepted:19 February 2024

Y. Tor ikai¹, G. Kikuchi¹, A. Owada¹, S. Masuzaki², T. Otsuka³, N. Ashikawa^2,4, M. Yajima², M. Tokitani², Y. Oya⁵, S.E. Lee⁶, Y. Hatano⁶, N. Asakura⁷, T. Hayashi⁸, M. Oyaidzu⁸, J. Likonen⁹, A. Widdowson¹⁰, M. Rubel^11,12

1 Ibaraki University Graduate School of Science and Engineering
2 National Institute for Fusion Science
3 Kindai University
4 SOKENDAI
5 Shizuoka University
6 Hydrogen Isotope Research Center
7 National Institute for Quantum and Radiological Science and Technology
8 National Institute for Quantum and Radiological Science and Technology
9 VTT Technical Research Centre of Finland
10 Culham Centre for Fusion Energy, United Kingdom Atomic Energy Authority
Abingdon OX14 3DB, United Kingdom of Great Britain and Northern Ireland
11 KTH Royal Institute of Technology
12 Uppsala University

Abstract
Divertor tiles after Joint European Torus-ITER like wall (JET-ILW) campaigns and dust collected after JET-C and JET-ILW operation were examined by a set of complementary techniques (full combustion and radiography) to determine the total, specific and areal tritium activities, poloidal tritium distribution in the divertor and the presence of that isotope in individual dust particles. In the divertor tiles, the majority of tritium is detected in the surface region and, the areal activities in the ILW divertor are in the 0.5–12 kBq cm⁻² range. The activity in the ILW dust is associated mainly with the presence of carbon particles being a legacy from the JET-C operation. The total tritium activities show significant differences between the JET operation with ILW and the earlier phase with the carbon wall (JET-C) indicating that tritium retention has been significantly decreased in the operation with ILW.

https://doi.org/10.1088/1741-4326/ad0c08
Accepted:13 November 2023

K. Miki ,^1,2 K. Kameya,^1,2 D. Sakai,^1,2 R. Urayama,^1,2 N. Imai,³ S. Ishikawa,⁴ S. Michimasa,³ S. Ota,³ M. Sasano,²H. Takeda,² T. Uesaka,² H. Haba,² M. Hara,⁵ Y. Hatano,⁵ T. Hayamizu,² N. Kobayashi,⁶ A. Tamii,⁶ S. Adachi,⁷ T. Chillery,³M. Dozono,^2,8 Y. Fujikawa,⁸ H. Fujita,⁶ N. Fukuda,² T. Furuno,⁶ J. Gao,⁹ S. Goto,¹⁰ S. Hanai,³ S. Hayakawa,³ Y.Hijikata,^2,8K. Himi,⁷ Y. Hirai,¹⁰ J.W. Hwang,¹¹ M. Ichimura,², D. Inomoto,¹⁰ M. Inoue,^1,2 H. Kasahara,¹⁰ T. Kawabata,^2,7K. Kishimoto,^2,10 S. Kitayama,^1,2 K. Kusaka,² J. Li,³ Y. Maeda,¹² Y. Maruta,^1,2 T. Matsui,^1,2 T. Matsuzaki,² S. Nakai,^1,2H. Nishibata,^2,10 M. Otake,² Y. Saito,^1,2 H. Sakai,² A. Sakaue,³ H. Sato,² K. Sekiguchi,1,2 Y. Shimizu,² S. Shimoura,³L. Stuhl,^2,11 T. Sumikama,² H. Suzuki,² R. Tsuji,^2,8 S. Tsuji,⁷ H. Umetsu,¹ Y. Utsuki,^1,2 T. Wakasa,¹⁰ A. Watanabe,^1,2K. Yako,³ Y. Yanagisawa,² N. Yokota,^2,10 C. Yonemura,^2,10 K. Yoshida,² and M.Yoshimoto²

1 Department of Physics, Tohoku University
2 RIKEN Nishina Center
3 Center for Nuclear Study, the University of Tokyo
4 Science Research Center, Hosei University
5 Hydrogen Isotope Research Center, University of Toyama,
6 Research Center for Nuclear Physics, Osaka University
7 Department of Physics, Osaka University
8 Department of Physics, Kyoto University
9 School of Physics, Peking University
10 Department of Physics, Kyushu University
11 Center for Exotic Nuclear Studies, Institute for Basic Science, Daejeon 34126, Republic of Korea
12 Faculty of Engineering, University of Miyazaki

Abstract
To search for low-energy resonant structures in isospin T =3/2 three-body systems, we have performed the experiments ³H（t,³He）3n and ³He（³He,t）3p at intermediate energies. For the 3n experiment, we have newly developed a thick Ti-³H target that has the largest tritium thickness among targets of this type ever made. The 3n experiment for the first time covered the momentum-transfer region as low as 15 MeV/c, which provides ideal conditions for producing fragile systems. However, in the excitation-energy spectra we obtained, we did not observe any distinct peak structures. This is in sharp contrast to tetraneutron spectra. The distributions of the 3n and 3p spectra are found to be similar, except for the displacement in energy due to Coulomb repulsion. Comparisons with theoretical calculations suggest that three-body correlations exist in the 3n and 3p systems, although not enough to produce a resonant peak.

DOI: 10.1103/PhysRevLett.133.012501
Accepted:accepted 6 May 2024