Sodium diffusion in hard carbon studied by small- and wide-angle neutron scattering and muon spin relaxation

Oishi, Kazuki*; Igarashi, Daisuke*; Tatara, Ryoichi*; Kawamura, Yukihiko*; Hiroi, Kosuke; Suzuki, Junichi*; Umegaki, Izumi*; Nishimura, Shoichiro*; Koda, Akihiro*; Komaba, Shinichi*; et al.

Journal of Physics; Conference Series, 2462, p.012048_1 - 012048_5, 2023/03

https://doi.org/10.1088/1742-6596/2462/1/012048

Atomic distribution and local structure in ice VII from in situ neutron diffraction

Yamashita, Keishiro*; Komatsu, Kazuki*; Klotz, S.*; Fabelo, O.*; Fernndez-Daz, M. T.*; Abe, Jun*; Machida, Shinichi*; Hattori, Takanori; Irifune, Tetsuo*; Shimmei, Toru*; et al.

Proceedings of the National Academy of Sciences of the United States of America, 119(40), p.e2208717119_1 - e2208717119_6, 2022/10

https://doi.org/10.1073/pnas.2208717119

Here we present the first elucidation of the disordered structure of ice VII, the dominant high-pressure form of water, at 2.2 GPa and 298 K from both single-crystal and powder neutron diffraction techniques. We reveal the three-dimensional atomic distributions from the maximum entropy method and unexpectedly find a ring-like distribution of hydrogen in contrast to the commonly-accepted discrete sites. In addition, total scattering analysis at 274 K clarified the difference in the intermolecular structure from ice VIII, the ordered counterpart of ice VII, despite an identical molecular geometry. Our complementary structure analyses robustly demonstrate the unique disordered structure of ice VII. Furthermore, these noble findings are related to the proton dynamics which drastically vary with pressure, and will contribute to an understanding of the structural origin of anomalous physical properties of ice VII under pressures.

Pressure dependence of ferromagnetic phase boundary in BaVSe studied with high-pressure SR

Sugiyama, Jun; Higemoto, Wataru; Andreica, D.*; Forslund, O. K.*; Nocerino, E.*; Mnsson, M.*; Sassa, Y.*; Gupta, R.*; Khasanov, R.*; Ota, Hiroto*; et al.

Physical Review B, 103(10), p.104418_1 - 104418_10, 2021/03

https://doi.org/10.1103/PhysRevB.103.104418

The magnetic nature of a quasi-one-dimensional compound, BaVSe, has been investigated with positive muon spin rotation and relaxation measurements at ambient and high pressures. At ambient pressure, the spectrum recorded under zero external magnetic field exhibited a clear oscillation below the Curie temperature due to the formation of quasistatic ferromagnetic order. As pressure increased from ambient pressure, was found to decrease slightly up to about 1.5 GPa, at which point started to increase rapidly with the further increase of the pressure. Based on a strong ferromagnetic interaction along the -axis, the result revealed that there are two magnetic interactions in the ab-plane.

Analysis for the accident at unit 1 of the Fukushima Daiichi NPS with THALES2/KICHE code in BSAF2 project

Tamaki, Hitoshi; Ishikawa, Jun; Sugiyama, Tomoyuki; Maruyama, Yu

Proceedings of 18th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-18) (USB Flash Drive), p.72 - 82, 2019/08

JAEA participated in the OECD/NEA BSAF2 project with our integrated severe accident analysis code, THALES2/KICHE, in order to analyze and discuss the accident progression and source term of the accident at the Fukushima Daiichi NPS. One of important characteristics of THALES2/KICHE code is that it has the capability of predicting iodine chemistry based on reaction kinetics in the aqueous phase. JAEA performed the three week analysis for the accident at unit 1 on the basis of the boundary conditions and assumptions proposed by the BSAF2 project and our own assumptions. In addition to the failure of the drywell, it was assumed in the present analysis that continuous leakage occurred through the containment venting line due to incomplete closing of valves in the line. The releases of fission products, especially for iodine and cesium, within three weeks after the earthquake were estimated to be approximately 6% and 1% of the initial inventory, respectively.

Analysis for the accident at Unit 3 of the Fukushima Daiichi NPS with THALES2/KICHE Code in BSAF2 project

Ishikawa, Jun; Tamaki, Hitoshi; Sugiyama, Tomoyuki; Maruyama, Yu

Proceedings of 18th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-18) (USB Flash Drive), p.536 - 547, 2019/08

Sensitivity analysis of source term in the accident of Fukushima Dai-ichi Nuclear Power Station Unit 1 using THALES2/KICHE

Tamaki, Hitoshi; Ishikawa, Jun; Sugiyama, Tomoyuki; Maruyama, Yu

Proceedings of Asian Symposium on Risk Assessment and Management 2018 (ASRAM 2018) (USB Flash Drive), 6 Pages, 2018/10

In the accidents at Fukushima Dai-ichi Nuclear Power Station, Tsunami caused loss of electric power supply and this event led to core melt and failure of Containment vessel. Finally, fission products were released to the environment. Currently, the activities for understanding of accident progressions are carried out based on the measured data during the accident, accident progression analysis using integrated severe accident analysis codes and investigation of inside of reactor buildings and containment vessels. On the other hand, there are some research activities with combination of accident progression analysis and accident consequence analysis. In Japan Atomic Energy Agency (JAEA), the research project of combination of these analyses using the computational simulation codes has been started. The results obtained from the combination analysis are expected to have broad width of uncertainty because of many uncertainty factors in this combined analysis. In order to perform the analysis efficiently, sensitivity analysis for failure location on containment vessel and its failure size were carried out by THALES2/KICHE developed by JAEA at first. This analysis was performed on unit 1, since it was the first plant to release radioactive materials to the environment during the accident and its consequence had no effect from other plants. The authors focused on the failure of containment vessel head flange, penetration seal and vacuum breaker pipe, and possibility of partial open of vent valve based on the investigations of reactor building inside performed by TEPCO. This paper presents the results obtained from this sensitivity analysis.

Severe accident scenario uncertainty analysis using the dynamic event tree method

Zheng, X.; Tamaki, Hitoshi; Ishikawa, Jun; Sugiyama, Tomoyuki; Maruyama, Yu

Proceedings of 14th International Conference on Probabilistic Safety Assessment and Management (PSAM-14) (USB Flash Drive), 10 Pages, 2018/09

Influence of chemical speciation in reactor cooling system on pH of suppression pool during BWR severe accident

Shiotsu, Hiroyuki; Ishikawa, Jun; Sugiyama, Tomoyuki; Maruyama, Yu

Journal of Nuclear Science and Technology, 55(4), p.363 - 373, 2018/04

https://doi.org/10.1080/00223131.2017.1403381

Energy-resolved small-angle neutron scattering from steel

Oba, Yojiro*; Morooka, Satoshi; Oishi, Kazuki*; Suzuki, Junichi*; Takata, Shinichi; Sato, Nobuhiro*; Inoue, Rintaro*; Tsuchiyama, Toshihiro*; Gilbert, E. P.*; Sugiyama, Masaaki*

Journal of Applied Crystallography, 50(2), p.334 - 339, 2017/04

https://doi.org/10.1107/S1600576717000279

Magnetic scattering in the simultaneous measurement of small-angle neutron scattering and Bragg edge transmission from steel

Oba, Yojiro*; Morooka, Satoshi; Oishi, Kazuki*; Sato, Nobuhiro*; Inoue, Rintaro*; Adachi, Nozomu*; Suzuki, Junichi*; Tsuchiyama, Toshihiro*; Gilbert, E. P.*; Sugiyama, Masaaki*

Journal of Applied Crystallography, 49(5), p.1659 - 1664, 2016/10

https://doi.org/10.1107/S1600576716013133