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Journal Articles

Simulation of a jet flow rectified by a grating-type structure using immersed boundary methods

Hirose, Yoshiyasu; Abe, Satoshi; Ishigaki, Masahiro*; Shibamoto, Yasuteru; Hibiki, Takashi*

Progress in Nuclear Energy, 169, p.105085_1 - 105085_13, 2024/04

Journal Articles

Critical heat flux for downward flows in vertical round pipes

Hirose, Yoshiyasu; Shibamoto, Yasuteru; Hibiki, Takashi*

Progress in Nuclear Energy, 168, p.105027_1 - 105027_17, 2024/03

Journal Articles

Development of a formulation to predict molten core spreading in an LWR severe accident

Sahboun, N. F.; Matsumoto, Toshinori; Iwasawa, Yuzuru; Wang, Z.; Sugiyama, Tomoyuki

Annals of Nuclear Energy, 195, p.110145_1 - 110145_12, 2024/01

Journal Articles

High-temperature rupture failure of high-burnup LWR-MOX fuel under a reactivity-initiated accident condition

Taniguchi, Yoshinori; Mihara, Takeshi; Kakiuchi, Kazuo; Udagawa, Yutaka

Annals of Nuclear Energy, 195, p.110144_1 - 110144_11, 2024/01

Journal Articles

Validation of the fast reactor plant dynamics analysis code Super-COPD using FFTF loss of flow without scram test #13

Hamase, Erina; Ohgama, Kazuya; Kawamura, Takumi*; Doda, Norihiro; Tanaka, Masaaki; Yamano, Hidemasa

Annals of Nuclear Energy, 195, p.110157_1 - 110157_14, 2024/01

To validate the fast reactor plant dynamics analysis code Super-COPD for the loss of flow without scram (LOFWOS) event, we participated in the IAEA benchmark for the LOFWOS test No.13 performed at the FFTF as one of the passive safety demonstration test. In the blind phase, there were challenges to reproduce outlet temperatures of fuel assemblies and the total reactivity. To improve the evaluation accuracy of them, the whole core model considering the radial heat transfer and interwrapper flow and the simplified assembly bowing reactivity model were introduced. As a result of the final phase, the second peak of outlet temperatures was reproduced successfully, and the total reactivity could generally follow the measured data. Super-COPD was validated for the LOFWOS event.

Journal Articles

Opposing mixed convection heat transfer for turbulent single-phase flows

Motegi, Kosuke; Shibamoto, Yasuteru; Hibiki, Takashi*; Tsukamoto, Naofumi*; Kaneko, Junichi*

International Journal of Energy Research, 2024, p.6029412_1 - 6029412_22, 2024/01

Convection, wherein forced and natural convections are prominent, is known as mixed convection. Specifically, when a forced convection flow is downward, this flow is called opposing flow. Several heat transfer correlations have been reported related to single-phase opposing flow; however, these correlations are based on experiments conducted in various channel geometries, working fluids, and thermal flow parameter ranges. Because the definition of nondimensional parameters and their validated range confirmed by experiments differ for each correlation reported in previous studies, establishing a guideline for deciding which correlation should be selected based on its range of applicability and extrapolation performance is important. This study reviewed the existing heat transfer correlations for turbulent opposing-flow mixed convection and the single-phase heat transfer correlations implemented in the thermal-hydraulic system codes. Furthermore, we evaluated the predictive performance of each correlation by comparing them with the experimental data obtained under various experimental conditions. The Jackson and Fewster, Churchill, and Swanson and Catton correlations (Int. J Heat Mass Transf., 1987) can accurately predict all the experimental data. The effect of the difference in the thermal boundary conditions, i.e., uniform heat flux and uniform wall temperature, on the turbulent mixed-convection heat transfer coefficient is not substantial. We confirmed that heat transfer correlations using the hydraulic-equivalent diameter as a characteristic length can be used for predictions regardless of channel-geometry differences. Furthermore, correlations described based on nondimensional dominant parameters can be used for predictions regardless of the differences in working fluids.

Journal Articles

Local structural changes in V-Ti-Cr alloy hydrides with hydrogen absorption/desorption cycling

Ikeda, Kazutaka*; Sashida, Sho*; Otomo, Toshiya*; Oshita, Hidetoshi*; Honda, Takashi*; Hawai, Takafumi*; Saito, Hiraku*; Ito, Shinichi*; Yokoo, Tetsuya*; Sakaki, Koji*; et al.

International Journal of Hydrogen Energy, 51(Part A), p.79 - 87, 2024/01

Journal Articles

Experiment and new analysis model simulating in-place cooling of a degraded core in severe accidents of sodium-cooled fast reactors

Imaizumi, Yuya; Aoyagi, Mitsuhiro; Kamiyama, Kenji; Matsuba, Kenichi; Akaev, A.*; Mikisha, A.*; Baklanov, V.*; Vurim, A.*

Annals of Nuclear Energy, 194, p.110107_1 - 110107_11, 2023/12

Journal Articles

Petrophysical properties of representative geological rocks encountered in carbon storage and utilization

Hu, Q.*; Wang, Q. M.*; Zhang, T.*; Zhao, C.*; Iltaf, K. H.*; Liu, S. Q.*; Fukatsu, Yuta

Energy Reports (Internet), 9, p.3661 - 3682, 2023/12

Journal Articles

Effect of molybdenum release on UO$$_{2}$$/MOX fuel oxidation under severe light water reactor accident conditions

Liu, J.; Miwa, Shuhei; Karasawa, Hidetoshi; Osaka, Masahiko

Nuclear Materials and Energy (Internet), 37, p.101532_1 - 101532_5, 2023/12

Journal Articles

Numerical interpretation of thermal desorption spectra of hydrogen from high-carbon ferrite-austenite dual-phase steel

Ebihara, Kenichi; Sekine, Daiki*; Sakiyama, Yuji*; Takahashi, Jun*; Takai, Kenichi*; Omura, Tomohiko*

International Journal of Hydrogen Energy, 48(79), p.30949 - 30962, 2023/09

To understand hydrogen embrittlement (HE), which is one of the stress corrosion cracking of steel materials, it is necessary to know the H distribution in steel, which can be effectively interpreted by numerical simulation of thermal desorption spectra. In weld metals and TRIP steels, residual austenite significantly influences the spectra, but a clear H distribution is not well known. In this study, an originally coded two-dimensional model was used to numerically simulate the previously reported spectra of high-carbon ferritic-austenitic duplex stainless steels, and it was found that H is mainly trapped at the carbide surface when the amount of H in the steel is low and at the duplex interface when the amount of H is high. It was also found that the thickness dependence of the H desorption peak for the interface trap site is caused by a different reason than the conventional one.

Journal Articles

3D water management in polymer electrolyte fuel cells toward fuel cell electric vehicles

Yoshimune, Wataru*; Higuchi, Yuki*; Kato, Akihiko*; Hibi, Shogo*; Yamaguchi, Satoshi*; Matsumoto, Yoshihiro*; Hayashida, Hirotoshi*; Nozaki, Hiroshi*; Shinohara, Takenao; Kato, Satoru*

ACS Energy Letters (Internet), 8(8), p.3485 - 3487, 2023/08

Journal Articles

Effect of interlayer K ordering on water intercalation behavior in $$delta$$-type layered manganese dioxide

Okamoto, Norihiko*; Yoshisako, Hiroki*; Ichitsubo, Tetsu

Energy Storage Materials, 61, p.102912_1 - 102912_9, 2023/08

Journal Articles

Inverse estimation scheme of radioactive source distributions inside building rooms based on monitoring air dose rates using LASSO; Theory and demonstration

Shi, W.*; Machida, Masahiko; Yamada, Susumu; Yoshida, Toru*; Hasegawa, Yukihiro*; Okamoto, Koji*

Progress in Nuclear Energy, 162, p.104792_1 - 104792_19, 2023/08

Predicting radioactive source distributions inside reactor building rooms based on monitoring air dose rates is one of the most essential steps towards decommissioning of nuclear power plants. However, the attempt is rather a difficult task, because it can be generally mapped onto mathematically ill-posed problem. Then, in order to successfully perform the inverse estimations on radioactive source distributions even in such ill-posed conditions, we suggest that a machine learning method, least absolute shrinkage and selection operator (LASSO) minimizing the loss function, $$||CP-Q||_2^2+lambda||_1$$ is a promising scheme. For the purpose of its feasibility demonstrations in real building rooms, we employ PHITS code to make LASSO input as the above matrix C connecting the radioactive source vector P defined on surface meshes of structural materials with the air dose rate vector Q measured at internal positions inside the rooms. We develop a mathematical criterion on the number of monitoring points to correctly predict source distributions based on the theory of Candes and Tao. Then, we confirm that LASSO actually shows extremely high possibility for source distribution reconstructions as far as the number of detection points satisfies our criterion. Moreover, we verify that radioactive hot spots can be truly reconstructed in an experiment setup. At last, we examine an influence factor like detector-source distance to enhance the predicting possibility in the inverse estimation. From the above demonstrations, we propose that LASSO scheme is a quite useful way to explore hot spots as seen in damaged nuclear power plants like Fukushima Daiichi nuclear power plants.

Journal Articles

Scalability of inertial particle deposition in bubbles with internal circulation

Motegi, Kosuke; Shibamoto, Yasuteru; Kukita, Yutaka

Annals of Nuclear Energy, 184, p.109679_1 - 109679_10, 2023/05

 Times Cited Count:0 Percentile:0.01(Nuclear Science & Technology)

Journal Articles

LASSO reconstruction scheme for radioactive source distributions inside reactor building rooms with spectral information and multi-radionuclide contaminated situations

Shi, W.*; Machida, Masahiko; Yamada, Susumu; Yoshida, Toru*; Hasegawa, Yukihiro*; Okamoto, Koji*

Annals of Nuclear Energy, 184, p.109686_1 - 109686_12, 2023/05

 Times Cited Count:1 Percentile:79.09(Nuclear Science & Technology)

Journal Articles

Generalized extreme value analysis of criticality tallies in Monte Carlo calculation

Ueki, Taro

Progress in Nuclear Energy, 159, p.104630_1 - 104630_9, 2023/05

 Times Cited Count:0 Percentile:0.01(Nuclear Science & Technology)

In this work, the methodology of Generalized Extreme Value (GEV) is applied to criticality tallies in Monte Carlo fission source cycles in order to evaluate the utility value of the distribution tail ends. Numerical results obtained under a sufficiently large number of particles per cycle show that the extreme value index (EVI) in GEV falls within the range of Weibull distribution including the EVI of Gumbel distribution as the role of a boundary value layer. GEV is also applied to a historically-challenging loosely-coupled system for demonstrating population diagnosis under an insufficient number of particles per cycle. It turns out that the transition from one equilibrium to other equilibrium makes the EVIs of upper and lower distribution tail ends depart from each other so that one of them falls in the range of Weibull distribution and the other in that of Frechet distribution.

Journal Articles

Mechanical properties of pure tungsten and tantalum irradiated by protons and neutrons at the Swiss spallation-neutron source

Saito, Shigeru; Suzuki, Kazuhiro; Obata, Hiroki; Dai, Y.*

Nuclear Materials and Energy (Internet), 34, p.101338_1 - 101338_9, 2023/03

 Times Cited Count:1 Percentile:35.78(Nuclear Science & Technology)

In this study, a post-irradiation examination of pure tungsten (W) and tantalum (Ta) specimens irradiated at the Swiss Spallation-Neutron Source is conducted. W is used as a potential candidate for a solid spallation-target material owing to its favorable properties. However, W also suffers from several disadvantages such as poor corrosion resistance to water coolant and irradiation embrittlement. To improve these properties, cladding technologies using Ta for W alloys have been developed. In the present study, we investigated the irradiation effects on two tungsten materials, poly-crystal W (W-Poly) and single-crystal W (W-Sin), along with pure polycrystalline Ta. The tensile-test results revealed that W-Poly exhibited almost no ductility after irradiation of 10.2-35.0 dpa. W-Sin was irradiated up to 10.2 dpa and demonstrated 6% of total elongation (TE). With regard to Ta, TE decreased based on the increase in irradiation, reaching almost zero at doses of more than 10.3 dpa.

Journal Articles

Feasibility study on reprocessing of HTGR spent fuel by existing PUREX plant and technology

Fukaya, Yuji; Goto, Minoru; Ohashi, Hirofumi

Annals of Nuclear Energy, 181, p.109534_1 - 109534_10, 2023/02

 Times Cited Count:0 Percentile:0.01(Nuclear Science & Technology)

Feasibility of reprocessing of High Temperature Gas-cooled Reactor (HTGR) spent fuel by existing Plutonium Uranium Redox EXtraction (PUREX) plant and technology has been investigated. The spent fuel dissolved solution includes approximately 3 times amount of uranium-235 and 1.5 times amount of protonium because of the 3 times higher burnup compared with that of Light Water Reactor (LWR). Then, the heavy metal of the spent fuel is planned to be diluted to 3.1 times by depleted uranium to satisfy the limitation of Rokkasho Reprocessing Plant (RRP) plant. In the present study, recoverability of uranium and plutonium with the dilution is confirmed by a simulation with a reprocessing process calculation code. Moreover, the case without the dilution from the economic perspective is investigated. As a result, the feasibility is confirmed without the dilution, and it is expected that the reprocessed amount is reduced to 1/3 compared with a diluted case even though the facility should be optimized from the perspective of mass flow and criticality.

Journal Articles

A Quantitative method of eutectic reaction study between boron carbide and stainless steel

Hong, Z.*; Pellegrini, M.*; Erkan, N.*; Liao, H.*; Yang, H.*; Yamano, Hidemasa; Okamoto, Koji*

Annals of Nuclear Energy, 180, p.109462_1 - 109462_9, 2023/01

 Times Cited Count:0 Percentile:0.01(Nuclear Science & Technology)

A series of experiments were conducted using B$$_{4}$$C material and SUS304 tubes as a simulant of the real control rods. Reaction rate constant data in the 1450K-1500K range were obtained, and are consistent with the reference values. The reaction layer microstructure observation and the associated chemical composition analysis were also carried onto the experiment samples.

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