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Journal Articles

Non-condensable gas accumulation and distribution due to condensation in the CIGMA Facility; Implications for Fukushima Daiichi Unit 3 (1F3)

Hamdani, A.; Soma, Shu; Abe, Satoshi; Shibamoto, Yasuteru

Progress in Nuclear Energy, 185, p.105771_1 - 105771_13, 2025/07

 Times Cited Count:0 Percentile:0.00(Nuclear Science & Technology)

JAEA Reports

Verification of analytical model of MELCOR code for accident of evaporation to dryness by boiling of reprocessed high level liquid waste

Yoshida, Kazuo; Hiyama, Mina*; Tamaki, Hitoshi

JAEA-Research 2025-003, 24 Pages, 2025/06

JAEA-Research-2025-003.pdf:2.06MB

An accident of evaporation to dryness by boiling of high-level radioactive liquid waste (HLLW) is postulated as one of the severe accidents caused by the loss of cooling function at a fuel reprocessing plant. In this case, volatile radioactive materials, such as ruthenium (RuO$$_{4}$$) are released from the tanks with water and nitric-acid mixed vapor into the atmosphere. Accurate quantitative estimation of released Ru is one of the important issues for risk assessment of those facilities. RuO$$_{4}$$ is expected to be absorbed chemically into water dissolving nitrous acid. Condensation of mixed vapor plays an important role for Ru transporting behavior in the facility building. The thermal-hydraulic behavior in the facility building is simulated with MELCOR code. The latent heat, which is a governing factor for vapor condensing behavior, has almost same value for nitric acid and water at the temperature range under 120 centigrade. Considering this thermal characteristic, it is assumed that the amount of nitric acid is substituted with mole-equivalent water in MELCOR simulation. Compensating modeling induced deviation by this assumption have been assembled with control function features of MELCOR. The comparison results have been described conducted between original simulation and modified simulation with compensating model in this report. It has been revealed that the total amount of pool water in the facility was as same as both simulations.

Journal Articles

Numerical investigation of the accuracy of a conductance-type wire-mesh sensor for a single spherical bubble and bubbly flow

Uesawa, Shinichiro; Ono, Ayako; Nagatake, Taku; Yamashita, Susumu; Yoshida, Hiroyuki

Journal of Nuclear Science and Technology, 62(5), p.432 - 456, 2025/05

 Times Cited Count:0 Percentile:0.00(Nuclear Science & Technology)

We performed electrostatic simulations of a wire-mesh sensor (WMS) for a single spherical bubble and bubbly flow to clarify the accuracy of the WMS. The electrostatic simulation for the single bubble showed the electric current density distribution and the electric current path from the excited transmitter to receivers for various bubble locations. It indicated systematic errors based on the nonuniform current density distribution around the WMS. The electrostatic simulation for the bubbly flow calculated by the computational fluid dynamics code, JAEA Utility Program for Interdisciplinary Thermal-hydraulics Engineering and Research (JUPITER), indicated that the WMS had difficulty in quantitatively measuring the intermediate values of the instantaneous void fraction between 0 and 1 because they cannot be estimated by previous transformation methods from the WMS signal to the void fraction, such as linear approximation or Maxwell's equation, and have a significant deviation of the void fraction of $$pm$$0.2 for the WMS signal. However, the electrostatic simulation indicated that the time-averaged void fractions around the center of the flow channel can be estimated using linear approximation, and the time-averaged void fraction near the wall of the flow channel can be estimated using Maxwell's equation.

Journal Articles

Neutronics-thermal-hydraulics-coupled transient analysis for reactor power change in an inclined offshore floating boiling water reactor

Fukuda, Kodai; Obara, Toru*; Suyama, Kenya

Nuclear Technology, 211(5), p.963 - 973, 2025/05

 Times Cited Count:0 Percentile:0.00(Nuclear Science & Technology)

Journal Articles

Role of solute hydrogen on mechanical property enhancement in Fe-24Cr-19Ni austenitic steel; An ${it in situ}$ neutron diffraction study

Ito, Tatsuya; Ogawa, Yuhei*; Gong, W.; Mao, W.*; Kawasaki, Takuro; Okada, Kazuho*; Shibata, Akinobu*; Harjo, S.

Acta Materialia, 287, p.120767_1 - 120767_16, 2025/04

 Times Cited Count:0 Percentile:0.00(Materials Science, Multidisciplinary)

Journal Articles

Stress and plastic strain partitioning behaviors and those contributions to martensitic transformation of retained austenite in medium manganese and transformation-induced plasticity-aided bainitic ferrite steels

Hojo, Tomohiko*; Koyama, Motomichi*; Kumai, Bakuya*; Zhou, Y.*; Shibayama, Yuki; Shiro, Ayumi*; Shobu, Takahisa; Saito, Hiroyuki*; Ajita, Saya*; Akiyama, Eiji*

ISIJ International, 65(2), p.284 - 296, 2025/02

Journal Articles

Construction of a Compton camera-equipped robotic system capable of moving autonomously towards the radiation source

Sato, Yuki; Kakuto, Takeshi*; Tanaka, Takayuki*; Shimano, Hiroyuki*

European Physical Journal; Special Topics, 10 Pages, 2025/00

 Times Cited Count:0 Percentile:0.00(Physics, Multidisciplinary)

Journal Articles

$$^{149}$$Sm synchrotron-radiation-based M$"{o}$ssbauer spectroscopy of Sm-based heavy fermion compounds

Tsutsui, Satoshi; Higashinaka, Ryuji*; Mizumaki, Masaichiro*; Kobayashi, Yoshio*; Nakamura, Jin*; Ito, Takashi; Yoda, Yoshitaka*; Matsuda, Tatsuma*; Aoki, Yuji*; Sato, Hideyuki*

Interactions (Internet), 245(1), p.9_1 - 9_10, 2024/12

Journal Articles

$$^{149}$$Sm synchrotron-radiation-based M$"{o}$ssbauer and $$mu^+$$SR studies of Sm$$_3$$Ru$$_4$$Ge$$_{13}$$

Tsutsui, Satoshi; Ito, Takashi; Nakamura, Jin*; Yoshida, Mio*; Kobayashi, Yoshio*; Yoda, Yoshitaka*; Nakamura, Jumpei*; Koda, Akihiro*; Higashinaka, Ryuji*; Aoki, Dai*; et al.

Interactions (Internet), 245(1), p.55_1 - 55_9, 2024/12

Journal Articles

Deep learning-based bubble detection with Swin Transformer

Uesawa, Shinichiro; Yoshida, Hiroyuki

Journal of Nuclear Science and Technology, 61(11), p.1438 - 1452, 2024/11

 Times Cited Count:0 Percentile:0.00(Nuclear Science & Technology)

We developed a deep learning-based bubble detector with a Shifted window Transformer (Swin Transformer) to detect and segment individual bubbles among overlapping bubbles. To verify the performance of the detector, we calculated its average precision (AP) with different number of training images. The mask AP increased with the increase in the number of training images when there were less than 50 images but remained constant when there were more than 50 images. It was observed that the AP for the Swin Transformer and ResNet were almost the same when there were more than 50 images; however, when few training images were used, the AP of the Swin Transformer were higher than that of the ResNet. Furthermore, with regard to the increase in void fraction, the AP of the Swin Transformer showed a decrease similar to that in the case of the ResNet; however, for few training images, the AP of the Swin Transformer was higher than that of the ResNet in all void fractions. Moreover, we confirmed the detector trained with synthetic bubble images was able to segment overlapping bubbles and deformed bubbles in a bubbly flow experiment. Thus, we verified that the new bubble detector with Swin Transformer provided higher AP than the detector with ResNet for fewer training images.

Journal Articles

Martensitic transformation-governed Luders deformation enables large ductility and late-stage strain hardening in ultrafine-grained austenitic stainless steel at low temperatures

Mao, W.*; Gao, S.*; Gong, W.; Kawasaki, Takuro; Ito, Tatsuya; Harjo, S.; Tsuji, Nobuhiro*

Acta Materialia, 278, p.120233_1 - 120233_13, 2024/10

 Times Cited Count:12 Percentile:87.44(Materials Science, Multidisciplinary)

Journal Articles

Enhancing mechanical properties of medium Mn steel by warm rolling based on laminated elemental segregation

Chen, H. F.*; Liu, B. X.*; Xu, P. G.; Fang, W.*; Tong, H. C.*; Yin, F. X.*

Journal of Materials Research and Technology, 32, p.3060 - 3069, 2024/09

 Times Cited Count:0 Percentile:0.00(Materials Science, Multidisciplinary)

JAEA Reports

Trial analysis of chemical behavior in high-level radioactive liquid waste tank at accident of evaporation to dryness by boiling of reprocessing plant

Yoshida, Kazuo; Hiyama, Mina*; Tamaki, Hitoshi

JAEA-Research 2024-007, 24 Pages, 2024/08

JAEA-Research-2024-007.pdf:2.1MB

An accident of evaporation to dryness by boiling of high-level radioactive liquid waste (HLLW) is postulated as one of the severe accidents caused by the loss of cooling function at a fuel reprocessing plant. In this case, volatile radioactive materials, such as ruthenium (Ru) are released from the tanks with water and nitric-acid mixed vapor into the atmosphere. Accurate quantitative estimation of released Ru is one of the important issues for risk assessment of those facilities. It has been observed experimentally that volatility of RuO$$_{4}$$ is suppressed by HNO$$_{2}$$ generated by HNO$$_{3}$$ radiolysis. The analysis of chemical reactions of NO$$_{x}$$ including HNO$$_{3}$$ and HNO$$_{2}$$ in the waste tank is essential to simulate of these phenomena. To resolve this issue, an analytical approach has been attempted to couple dynamically two computer codes SHAWED and SCHERN. The simulation of boiling behavior in the tank is conducted with SHAWED. SCHERN simulates chemical behaviors of HNO$$_{3}$$, HNO$$_{2}$$ and NO$$_{x}$$ in the tank. A programmatic coupling algorithm and a trial simulation of the accident are presented in this report.

Journal Articles

Thermal stability of retained austenite with heterogeneous composition and size in austempered Fe-2Mn-1.5Si-0.4C alloy

Watanabe, Miku*; Miyamoto, Goro*; Zhang, Y.*; Morooka, Satoshi; Harjo, S.; Kobayashi, Yasuhiro*; Furuhara, Tadashi*

ISIJ International, 64(9), p.1464 - 1476, 2024/07

 Times Cited Count:2 Percentile:63.37(Metallurgy & Metallurgical Engineering)

Journal Articles

Proposal of negative stress ratio R for fatigue crack growth rates of austenitic stainless steels in air for ASME Code Section XI based on trend in experimental data

Negyesi, M.*; Yamaguchi, Yoshihito; Hasegawa, Kunio; Lacroix, V.*; Morley, A.*

Proceedings of ASME 2024 Pressure Vessels & Piping Conference (PVP 2024) (Internet), 8 Pages, 2024/07

Journal Articles

Analysis of the stress field around concealed active fault from minor faults-slip data collected by geological survey; An Example in the 1984 Western Nagano Earthquake region

Nishiyama, Nariaki; Nakajima, Toru; Goto, Akira*; Hakoiwa, Hiroaki; Nagata, Mitsuhiro; Shimada, Koji; Niwa, Masakazu

Earth and Space Science (Internet), 11(6), p.e2023EA003360_1 - e2023EA003360_15, 2024/06

 Times Cited Count:0 Percentile:0.00(Astronomy & Astrophysics)

Earthquakes with magnitudes of 6-7 have been reported even in various active tectonic settings where fault deformation topography have not been detected. Therefore, delineating concealed active faults generating such earthquakes is necessary to reduce earthquake damage; however, few studies exist to provide its clues regarding such faults. The 1984 Western Nagano Earthquake in Japan was a main shock with a magnitude of Mj 6.8 and a depth of 2 km at the source. Solid bedrocks are well-exposed in the earthquake source region; however, no surface rupture have been identified, and the active fault is known to be concealed. In this study, we collected data on striations observed in fractures by geological survey around the source area of the 1984 Western Nagano Earthquake. Using the collected data, the multiple inverse method was used to estimate the stresses that affected the striation formation. Consequently, stresses similar to acting faults in this area were detected in minor faults around the known concealed active fault. This suggests that the minor faults might be part of the damage zone that has been developed around the concealed active fault. Some minor faults were recognized in Quaternary volcanic rocks, confirming that they experienced displacements recently. This study indicates the possibility of detecting concealed active faults in the bedrock by geological survey.

Journal Articles

Validation of the hybrid turbulence model in detailed thermal-hydraulic analysis code SPIRAL for fuel assembly using sodium experiments data of 37-pin bundles

Yoshikawa, Ryuji; Imai, Yasutomo*; Kikuchi, Norihiro; Tanaka, Masaaki; Ohshima, Hiroyuki

Nuclear Technology, 210(5), p.814 - 835, 2024/05

 Times Cited Count:0 Percentile:0.00(Nuclear Science & Technology)

In the study of safety enhancement on advanced sodium-cooled fast reactor, it is essential to clarify the thermal-hydraulics under various operation conditions in a fuel assembly (FA) with the wire-wrapped fuel pins to assess the structural integrity of the fuel pin. A finite element thermal-hydraulics analysis code named SPIRAL has been developed to analyze the detailed thermal-hydraulics phenomena in a FA. In this study, the numerical simulations of the 37-pin bundle sodium experiments at different Re number conditions, including a transitional condition between laminar and turbulent flows and turbulent flow conditions, were performed to validate the hybrid turbulence model equipped in SPIRAL. The temperature distributions predicted by SPIRAL was consistent with those measured in the experiments. Through the validation study, the applicability of the hybrid turbulence model in SPIRAL to thermal-hydraulic evaluation of sodium-cooled FA in the wide range of Re number was confirmed.

Journal Articles

Dynamic deformation properties of medium-Mn multi-phase steels containing retained austenite

Okitsu, Takayuki*; Hojo, Tomohiko*; Morooka, Satoshi; Miyamoto, Goro*

Tetsu To Hagane, 110(3), p.260 - 267, 2024/02

 Times Cited Count:0 Percentile:0.00(Metallurgy & Metallurgical Engineering)

Journal Articles

Direct observation of concentration fluctuations in Au-Si eutectic liquid by small-angle neutron scattering

Sakaguchi, Yoshifumi*; Takata, Shinichi; Kawakita, Yukinobu; Fujimura, Yuki; Kondo, Keietsu

Journal of Physics; Condensed Matter, 35(41), p.415403_1 - 415403_11, 2023/10

 Times Cited Count:0 Percentile:0.00(Physics, Condensed Matter)

683 (Records 1-20 displayed on this page)