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Wada, Yuki; Shibamoto, Yasuteru; Hibiki, Takashi*
International Journal of Heat and Mass Transfer, 239, p.126598_1 - 126598_18, 2025/04
elik, Y.*; Stankovskiy, A.*; Iwamoto, Hiroki; Iwamoto, Yosuke; Van den Eynde, G.*
Annals of Nuclear Energy, 212, p.111048_1 - 111048_12, 2025/03
Times Cited Count：0Guembou Shouop, C.; Tsuchiya, Harufumi
Nuclear Instruments and Methods in Physics Research A, 1072, p.170189_1 - 170189_14, 2025/03
Lee, J.; Rossi, F.; Kodama, Yu; Hironaka, Kota; Koizumi, Mitsuo; Sano, Tadafumi*; Matsuo, Yasunori*; Hori, Junichi*
Annals of Nuclear Energy, 211, p.111017_1 - 111017_7, 2025/02
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)Brumm, S.*; Gabrielli, F.*; Sanchez Espinoza, V.*; Stakhanova, A.*; Groudev, P.*; Petrova, P.*; Vryashkova, P.*; Ou, P.*; Zhang, W.*; Malkhasyan, A.*; et al.
Annals of Nuclear Energy, 211, p.110962_1 - 110962_16, 2025/02
Times Cited Count：1 Percentile：0.00(Nuclear Science & Technology)Motegi, Kosuke; Shibamoto, Yasuteru; Hibiki, Takashi*
International Journal of Heat and Mass Transfer, 237, p.126406_1 - 126406_15, 2025/02
Times Cited Count：0Sun, Haomin; Hibiki, Takashi*
International Journal of Heat and Mass Transfer, 237, p.126445_1 - 126445_14, 2025/02
Schaar, K.*; Spiegl, T.*; Sato, Tatsuhiko; Langematz, U.*
Journal of Environmental Radioactivity, 282, p.107592_1 - 107592_14, 2025/02
Abe, Yosuke; Tsuru, Tomohito; Fujita, Yohei*; Otomo, Masahide*; Sasaki, Taisuke*; Yamashita, Shinichiro; Okubo, Nariaki; Ukai, Shigeharu
Journal of Nuclear Materials, 606, p.155606_1 - 155606_12, 2025/02
We investigated the effect of Al addition on the formation of 
phase in Fe-Cr-Al model alloys by thermal aging. The Vickers hardness tests and a machine learning model indicate that the formation of the phase is promoted by low Al additions and suppressed by high Al additions. First-principles calculations, which indicate that Cr-Al-vacancy pairs are more stable than Cr-Cr pairs and that including Al atoms during phase nucleation may be energetically advantageous. On the other hand, the formation of Al-Al pairs was very unstable. The formation of Al-Al pairs near the interface can be avoided when the amount of Al addition is small. However, it is inevitable when the amount of Al addition is significant, leading to the instability of the phase.
Matsushita, Kentaro; Ezure, Toshiki; Tanaka, Masaaki; Imai, Yasutomo*; Fujisaki, Tatsuya*; Sakai, Takaaki*
Nuclear Engineering and Design, 432, p.113785_1 - 113785_16, 2025/02
Establishing an evaluation method for the gas entrainment (GE) of argon cover gas due to surface vortices is required in terms of safety design of sodium-cooled fast reactors. To modify the evaluation model in an in-house evaluation tool for GE, StreamViewer, a modified evaluation model on the pressure distribution along the vortex center line (PVL model) was proposed to identify the vortex center lines by connecting continuous vortex center points from the suction port to the surface and evaluate gas core length based on the balance between the hydrostatic pressure and the pressure decrease distribution along the vortex center line. PVL model was applied the three-dimensional numerical analysis results for the experiments where a plate induced unsteady traveling vortices in the open channel flow. Consequently, the GE evaluation using StreamViewer with PVL model could reproduce the relation between the inlet flow velocity and the gas core length in the unsteady vortex flow experiments.
Matsumura, Taichi; Okumura, Keisuke; Sakamoto, Masahiro; Terashima, Kenichi; Riyana, E. S.; Kondo, Kazuhiro*
Nuclear Engineering and Design, 432, p.113791_1 - 113791_9, 2025/02
Hamase, Erina; Miyake, Yasuhiro*; Imai, Yasutomo*; Doda, Norihiro; Ono, Ayako; Tanaka, Masaaki
Nuclear Engineering and Design, 432, p.113738_1 - 113738_12, 2025/02
To enhance the safety of sodium-cooled fast reactors, the natural circulation (NC) decay heat removal systems with a dipped-type direct heat exchanger (D-DHX) have been investigated. During the D-DHX operation, since the core-plenum interaction occurs, the reactor vessel model using a computational fluid dynamics code (RV-CFD) is required to be established. Previously, the CFD model based on the subchannel analysis was developed. In this study, to achieve lower computational cost maintaining the prediction accuracy, the coarse-mesh subchannel CFD (CMSC) model was developed, and was incorporated into the core of RV-CFD. As a result of PLANDTL-1 test analysis, the RV-CFD with the CMSC model can reproduce the core-plenum interaction under NC conditions.
Onishi, Takashi; Koyama, Shinichi*; Yokoyama, Keisuke; Morishita, Kazuki; Watanabe, Masashi; Maeda, Shigetaka; Yano, Yasuhide; Oki, Shigeo
Nuclear Engineering and Design, 432, p.113755_1 - 113755_17, 2025/02
Satou, Akira; Hibiki, Takashi*; Ikeda, Ryo; Shibamoto, Yasuteru
Progress in Nuclear Energy, 180, p.105593_1 - 105593_11, 2025/02
During a loss-of-coolant accident in a pressurized water reactor (PWR), there is a risk that pressurized thermal shock (PTS) may occur on the internal wall of the reactor pressure vessel (RPV) due to the flow of emergency core cooling (ECC) water injected into the cold leg that flows into the downcomer. PTS is caused by the rapid cooling of the downcomer wall by the ECC water and is strongly influenced by the temperature of the ECC water, the collision position and velocity of the water jet on the wall, the velocity of the liquid film on the wall, the thickness of the liquid film, and the spread of the downward flow. Therefore, the flow of ECC water discharging from the cold leg to the downcomer may strongly impact PTS events. To help understand this flow phenomenon, we reviewed studies on free outflow from a circular pipe. Experimental findings on the classification of flow conditions, transition conditions between flow conditions, end depth ratio, free surface profile of flow in the circular pipe, and shape of the nappe flowing out from the pipe have been obtained in a form that is almost consistent with each other. In contrast, when considering the flow from the cold leg to the downcomer, it is necessary to deal with the flow field in a specific situation, such as the flow into a narrow gap rather than a free space, the existence of rounded corners at the outlet of the circular pipe, and the influence of steam flow flowing from the core to the cold leg. However, few previous studies consider these factors, so we summarized them as knowledge that needs to be accumulated in the future.
Wakasa, Sachi*; Ishiyama, Tatsuya*; Hirouchi, Daisuke*; Matta, Nobuhisa*; Fujita, Natsuko; Echigo, Tomoo*
Geomorphology, 468, p.109497_1 - 109497_8, 2025/01
Times Cited Count：0To estimate long-term rates of coastal uplift along the northern Pacific coast of Northeast Japan, we determined the surface exposure ages of marine and fluvial terraces based on terrestrial in situ cosmogenic radionuclide dating of exposed bedrock surfaces. Based on reinterpretation of marine and fluvial terraces, we collected samples from the northern and southern Sanriku coast. The surface exposure ages from 
Be concentrations in quartz calculated from the measured Be/
Be ratios commonly suggest middle to late Pleistocene ages for the marine and fluvial terraces and slow coastal uplift rates at intermediate timescales. The results demonstrate different styles of crustal strain accommodation in the northern Northeast Japan arc above the subducting Pacific plate.
Fukada, Yukimasa; Aoyagi, Yumito*; Yokoyama, Misaki*; Horibe, Yoichi*; Kano, Jun*; Kaneda, Miyu*; Fujii, Tatsuo*; Yoshigoe, Akitaka; Kobata, Masaaki; Fukuda, Tatsuo; et al.
Journal of Electronic Materials, 54, p.686 - 692, 2025/01
no abstracts in English
Nakamura, Satoshi; Ishii, Sho*; Kato, Hitoshi*; Ban, Yasutoshi; Hiruta, Kenta; Yoshida, Takuya; Uehara, Hiroyuki; Obata, Hiroki; Kimura, Yasuhiko; Takano, Masahide
Journal of Nuclear Science and Technology, 62(1), p.56 - 64, 2025/01
A dissolution method for analyzing the elemental composition of fuel debris using the sodium peroxide (Na
O) fusion technique has been developed. Herein, two different types of simulated debris materials (such as solid solution of (Zr,RE)O and molten core-concrete interaction products (MCCI)) were taken. At various temperatures, these debris materials were subsequently fused with NaO in crucibles, which are made of different materials, such as Ni, AlO
, Fe, and Zr. Then, the fused samples are dissolved in nitric acid. Furthermore, the effects of the experimental conditions on the elemental composition analysis were evaluated using inductively coupled plasma-atomic emission spectroscopy (ICP-AES), which suggested the use of a Ni crucible at 923 K as an optimum testing condition. The optimum testing condition was then applied to the demonstration tests with Three Mile Island unit-2 (TMI-2) debris in a shielded concrete cell, thereby achieving complete dissolution of the debris. The elemental composition of TMI-2 debris revealed by the proposed dissolution method has good reproducibility and has an insignificant contradiction in the mass balance of the sample. Therefore, this newly developed reproducible dissolution method can be effectively utilized in practical applications by dissolving fuel debris and estimating its elemental composition.
Yoshida, Masato; Iguchi, Satoshi; Hirano, Hiroshi*; Kitamura, Akihiro
Nuclear Engineering and Design, 431, p.113691_1 - 113691_16, 2025/01
Times Cited Count：0The Plutonium Fuel Fabrication Facility is currently in the decommissioning phase, with glovebox dismantling operations ongoing since 2010. During conventional glovebox dismantling operations, the glovebox to be dismantled is enclosed within plastic tents to contain contamination. The glovebox is then dismantled by workers wearing air-fed suits with thermal or mechanical cutting tools, which typically generate dross or sparks in the form of radioactive aerosols during cutting. Despite the longevity and meticulous organization of this manual method, the workload remains considerable, while the allowable working time is limited. In addition, the potential for inhalation exposure to plutonium is elevated in the event of an accident given the contamination of the work area. To overcome disadvantages associated with conventional glovebox dismantling methods, new methods are currently being developed. The primary objective is to reduce the reliance on operation based on air-fed suits and enhance worker safety by introducing remote equipment and a new floor-reinforcing panel. Another objective is to suppress waste generation by reusing all equipment on multiple occasions which is achieved by developing a containment system that have a large open port with a pallet for the storage and reuse of equipment for successive operations. Furthermore, a glove operation compartment is designed and tested for the manual handling of dismantled materials as an additional strategy to reduce work based on air-fed suits and mitigate secondary waste generation.
Sr/Y inside the Fukushima Daiichi Nuclear Power Station Unit 3 reactor building using a liquid light guide Cherenkov counterTerasaka, Yuta; Sato, Yuki; Furuta, Yoshihiro*; Kubo, Shin*; Ichiba, Yuta*
Nuclear Instruments and Methods in Physics Research A, 1070(2), p.170021_1 - 170021_9, 2025/01
Times Cited Count：0 Percentile：0.00(Instruments & Instrumentation)Somekawa, Toshihiro*; Kurahashi, Shinri*; Matsuda, Shohei; Yogo, Akifumi*; Kuze, Hiroaki*
Optics Letters, 50(1), p.57 - 60, 2025/01
