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Horiguchi, Naoki; Yoshida, Hiroyuki; Kaneko, Akiko*; Abe, Yutaka*
Proceedings of 12th Japan-Korea Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS12) (Internet), 6 Pages, 2022/10
For safety evaluation of nuclear reactors in severe accidents, it is important to estimate physical quantities of fragments generated from the molten fuel jet, which falls in a pool and breaks up. The evaluation method has been developed for the behavior as liquid jet with hydrodynamic interaction including fuel coolant interaction (FCI). In case of a shallow pool assumed in ex-vessel, the molten fuel jet is assumed to behave as wall-impinging liquid jet and to form liquid film flow spreading on the floor with/without fragmentation. In our research, focusing on hydrodynamic interaction and the transient 3-dimensional spreading on the floor, we have developed the evaluation method by numerical simulation using the two-phase flow simulation code with interface tracking method (TPFIT) developed by JAEA and, the experimental method using the 3D-LIF method in liquid-liquid system for the validation data. In our previous studies, we investigated the wall-impinging liquid jet behavior with fragmentation and observed that the liquid film flow had some characteristic parts transiently. Since it indicates that the quantities change depending on the parts and affect the safety evaluation, it is important to measure the quantities of the fragments generated from each part. This paper explains the measurement of the physical quantities of the fragments generated from each part of the wall-impinging liquid jet in a shallow pool for the validation of the numerical simulation. We conducted an experiment with the 3D-LIF method and segmented the experimental data based on the fragmentation point over the liquid film flow using the dispersed phase tracking method, developed by JAEA. Then, we measured the diameter and amount of the fragments from the segmented experimental data and investigated their changing trend.
Takatsuka, Daichi*; Morita, Koji*; Liu, W.*; Zhang, T.*; Nakamura, Takeshi*; Kamiyama, Kenji
Proceedings of 12th Japan-Korea Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS12) (Internet), 10 Pages, 2022/10
Yamamura, Sota*; Fujiwara, Kota*; Honda, Kota*; Yoshida, Hiroyuki; Horiguchi, Naoki; Kaneko, Akiko*; Abe, Yutaka*
Physics of Fluids, 34(8), p.082110_1 - 082110_13, 2022/08
Times Cited Count：2 Percentile：41.08(Mechanics)Liquid spreading and atomization due to jet impingement in liquid-liquid systems are considered to be crucial for understanding the cooling behavior of high-temperature molten material in a shallow water pool. This phenomenon takes place when a liquid jet enters a pool filled with other immiscible liquid. The jet spreads radially after impinging on the floor while forming a thin liquid film and atomizing droplets. In this paper, we explain the result to quantify the unsteady three-dimensional behavior of the spreading jet by the employment of 3D-LIF measurements and 3-dimensional reconstruction. Under high flow velocity conditions, the phenomena of hydraulic jump and atomization of the liquid film occurred along with the spreading. To evaluate the spreading behavior, a comparison of the jump radius position of the liquid-liquid system as the representative value was made with the one calculated by the existing theory of a gas-liquid system. As the result, the spreading of the liquid film in the liquid-liquid system was suppressed compared with that in the gas-liquid system. Furthermore, the PTV method was successfully used to measure the velocity boundary layer and velocity profile in the liquid film, which are important factors that affect the spreading mechanism of the liquid film. These results revealed that in liquid-liquid systems, shear stress at the liquid-liquid interface causes a decrease in the flow velocity and suppressed the development of the velocity boundary layer. Also, to evaluate the atomization behavior, the number and diameter distribution of the droplets were measured from the acquired 3-dimensional shape data of the jet. As the result, the number of droplets increased with the flow velocity. Based on these results, we concluded that the spreading of the liquid film is affected by such atomization behavior.
Ichihara, Yoshitaka*; Nakamura, Naohiro*; Nabeshima, Kunihiko*; Choi, B.; Nishida, Akemi
Kozo Kogaku Rombunshu, B, 68B, p.271 - 283, 2022/04
This paper aims to evaluate the applicability of the equivalent linear analysis method for reinforced concrete, which uses frequency-independent hysteretic damping, to the seismic design of reactor building of the nuclear power plant. To achieve this, we performed three-dimensional FEM analyses of the soil-structure interaction system, focusing on the nonlinear and equivalent linear seismic behavior of a reactor building under an ideal soil condition. From these results, the method of equivalent analysis showed generally good correspondence with the method of the nonlinear analysis, confirming the effectiveness. Moreover, the method tended to lower the structural stiffness compared to the nonlinear analysis model. Therefore, in the evaluation of the maximum shear strain, we consider that the results were more likely to be higher than the results of nonlinear analysis.
Collaborative Laboratories for Advanced Decommissioning Science; Osaka University*
JAEA-Review 2021-046, 77 Pages, 2022/01
JAEA-Review-2021-046.pdf:2.92MB
The Collaborative Laboratories for Advanced Decommissioning Science (CLADS), Japan Atomic Energy Agency (JAEA), had been conducting the Nuclear Energy Science & Technology and Human Resource Development Project (hereafter referred to "the Project") in FY2020. The Project aims to contribute to solving problems in the nuclear energy field represented by the decommissioning of the Fukushima Daiichi Nuclear Power Station, Tokyo Electric Power Company Holdings, Inc. (TEPCO). For this purpose, intelligence was collected from all over the world, and basic research and human resource development were promoted by closely integrating/collaborating knowledge and experiences in various fields beyond the barrier of conventional organizations and research fields. The sponsor of the Project was moved from the Ministry of Education, Culture, Sports, Science and Technology to JAEA since the newly adopted proposals in FY2018. On this occasion, JAEA constructed a new research system where JAEA-academia collaboration is reinforced and medium-to-long term research/development and human resource development contributing to the decommissioning are stably and consecutively implemented. Among the adopted proposals in FY2018, this report summarizes the research results of the "Development of technology to simultaneously measure viscosity and surface tension of molten materials in reactor core" conducted from FY2018 to FY2020. Since the final year of this proposal was FY2020, the results for three fiscal years were summarized. Since (U, Zr)O
and boride, molten materials in reactor core, exist at extremely high temperature, chemical reactions between the vessel and these molten materials are unavoidable. Therefore, it is difficult to measure the thermophysical property of these materials. In the present study, droplets are produced by heating and melting the samples levitated by a gas levitation method, then the droplets are collided with a substrate.
Sakai, Kenji; Oku, Takayuki; Okudaira, Takuya; Kai, Tetsuya; Harada, Masahide; Hiroi, Kosuke; Hayashida, Hirotoshi*; Kakurai, Kazuhisa*; Shimizu, Hirohiko*; Hirota, Katsuya*; et al.
JPS Conference Proceedings (Internet), 33, p.011116_1 - 011116_6, 2021/03
In neutron fundamental physics, study of correlation term 
of a neutron spin 
and a target nuclear spin 
is important because term interferes to parity non-conserving (PNC) and time reversal non-conserving terms. For this study, a xenon (Xe) is an interesting nucleus because it has been observed an enhancement of PNC effect around neutron resonance peaks, and polarizes up to 
by using a spin exchange optical pumping (SEOP) method. We would plan to develop a polarized Xe gas target with a compact in-situ SEOP system, and to study term by utilizing epithermal neutron beams supplied from a high intense pulsed spallation neutron source. As the first step, we attempted to measure neutron polarizing ability caused by term at a 9.6 eV s-wave resonance peak of 
Xe at BL10 in MLF, by detecting change 
of ratio between neutron transmissions with the polarized and unpolarized Xe target. After demonstrating that our apparatus could detect small change (
) of neutron transmissions caused by Doppler broadening effect, a signified value of has been obtained as preliminary results. For analyzing the obtained in detail, we are improving our nuclear magnetic resonance and electron paramagnetic resonance systems for evaluating Xe polarization independently of neutron beams.
Collaborative Laboratories for Advanced Decommissioning Science; Osaka University*
JAEA-Review 2020-038, 41 Pages, 2020/12
JAEA-Review-2020-038.pdf:3.28MB
JAEA/CLADS had been conducting the Nuclear Energy Science & Technology and Human Resource Development Project in FY2019. Among the adopted proposals in FY2018, this report summarizes the research results of the "Development of Technology to Simultaneously Measure Viscosity and Surface Tension of Molten Materials in Reactor Core" conducted in FY2019.
Collaborative Laboratories for Advanced Decommissioning Science; Osaka University*
JAEA-Review 2019-025, 36 Pages, 2020/01
JAEA-Review-2019-025.pdf:2.57MB
CLADS, JAEA, had been conducting the Center of World Intelligence Project for Nuclear Science/Technology and Human Resource Development (hereafter referred to "the Project") in FY2018. The Project aims to contribute to solving problems in nuclear energy field represented by the decommissioning of the Fukushima Daiichi Nuclear Power Station, Tokyo Electric Power Company Holdings, Inc. For this purpose, intelligence was collected from all over the world, and basic research and human resource development were promoted by closely integrating/collaborating knowledge and experiences in various fields beyond the barrier of conventional organizations and research fields. The sponsor of the Project was moved from the Ministry of Education, Culture, Sports, Science and Technology to JAEA since the newly adopted proposals in FY2018. On this occasion, JAEA constructed a new research system where JAEA-academia collaboration is reinforced and medium-to-long term research/development and human resource development contributing to the decommissioning are stably and consecutively implemented. Among the adopted proposals in FY2018, this report summarizes the research results of the "Development of Technology to Simultaneously Measure Viscosity and Surface Tension of Molten Materials in Reactor Core". Since (U,Zr)O and boride, molten materials in reactor core, exist at extremely high temperature, chemical reactions between the vessel and these molten materials are unavoidable. Therefore, it is difficult to measure the thermophysical property of these materials. In the present study, droplets are produced by heating and melting the samples levitated by a gas levitation method, then the droplets are collided with a substrate. From the instant behavior of the collision, a new technology to simultaneously derive the viscosity and surface tension will be developed.
Sato, Ikken
Journal of Nuclear Science and Technology, 56(5), p.394 - 411, 2019/05
Times Cited Count：10 Percentile：74.6(Nuclear Science & Technology)Water columns were adopted in the pressure measurement system of Fukushima-Daiichi Unit-3. Part of these water columns evaporated during the accident condition jeopardizing correct understanding on actual pressure. Through comparison of RPV (Reactor Pressure Vessel) and S/C pressures with D/W pressure, such water-column effect was evaluated. Correction for this effect was developed enabling clarification of slight pressure difference among RPV, S/C and D/W. This information was then integrated with other available data such as, water level, CAMS and environmental dose rate, into an interpretation of accident focusing on RPV and PCV pressurization/depressurization and radioactive material release to environment. It is suggested that dryout of in-vessel and ex-vessel debris was likely causing pressure decrease. S/C water poured into pedestal heated by relocated debris was the likely cause of pressurization. Cyclic reflooding of pedestal debris and dryout was likely.
Nagaya, Yasunobu; Adachi, Masaaki*
Proceedings of International Conference on Mathematics & Computational Methods Applied to Nuclear Science & Engineering (M&C 2017) (USB Flash Drive), 6 Pages, 2017/04
MVP is a general-purpose Monte Carlo code for neutron and photon transport calculations based on the continuous-energy method. To speed up the MVP code, hybrid parallelization is applied with a message passing interface library MPI and a shared-memory multiprocessing library OpenMP. The performance test has been done for an eigenvalue calculation of a fast reactor subassembly, a fixed-source calculation of a neutron/photon coupled problem and a PWR full core model. Comparisons has been made for MPI only with 4 processes and hybrid parallelism with 4 processes 
3 threads. As a result, the hybrid parallelism yields the reduction of elapsed time by 16% to 34% and the used memories are almost the same.
Matsuba, Kenichi; Isozaki, Mikio; Kamiyama, Kenji; Suzuki, Toru; Tobita, Yoshiharu
Proceedings of 11th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, Operation and Safety (NUTHOS-11) (USB Flash Drive), 8 Pages, 2016/10
In order to evaluate the distance for fragmentation of molten core material discharged into the lower sodium plenum during core disruptive accidents in sodium-cooled fast reactors, experiments with simulated molten materials and coolants (water, sodium) was carried out, where an empirical correlation of the distance for fragmentation was developed. The empirical correlation developed by this study showed a good agreement with the measurement results obtained by the present experiments. It was found that in order to well-predict the distance for fragmentation in sodium, thermal phenomena, such as sodium boiling and resultant vapor expansion, needed to be considered.
Furuta, Takuya; Sato, Tatsuhiko; Ogawa, Tatsuhiko; Niita, Koji*; Ishikawa, Kenichi*; Noda, Shigeho*; Takagi, Shu*; Maeyama, Takuya*; Fukunishi, Nobuhisa*; Fukasaku, Kazuaki*; et al.
Proceedings of Joint International Conference on Mathematics and Computation, Supercomputing in Nuclear Applications and the Monte Carlo Method (M&C + SNA + MC 2015) (CD-ROM), 9 Pages, 2015/04
In Particle and Heavy Ion Transport code System PHITS, two parallel computing functions are prepared to reduce the computational time. One is the distributed-memory parallelization using message passing interface (MPI) and the other is the shared-memory parallelization using OpenMP directives. Each function has advantages and disadvantages, and thus, by adopting both functions in PHITS, it is possible to conduct parallel computing suited for needs of users. It is also possible to conduct the hybrid parallelization by the intra-node OpenMP parallelization and the inter-node MPI parallelization in supercomputer systems. Each parallelization functions were explained together with some application results obtained using a workstation and a supercomputer system, K computer at RIKEN.
Matsuda, Norihiro
Hoshasen Shahei Handobukku; Kisohen, p.229 - 288, 2015/03
no abstracts in English
Kusakabe, Toshio*; Shiota, Kenji*; Kubo, Hirotaka; Shirai, Toshizo*
Journal of Plasma and Fusion Research SERIES, Vol.7, p.237 - 239, 2006/00
no abstracts in English
plasma operationTamai, Hiroshi; Akiba, Masato; Azechi, Hiroshi*; Fujita, Takaaki; Hamamatsu, Kiyotaka; Hashizume, Hidetoshi*; Hayashi, Nobuhiko; Horiike, Hiroshi*; Hosogane, Nobuyuki; Ichimura, Makoto*; et al.
Nuclear Fusion, 45(12), p.1676 - 1683, 2005/12
Times Cited Count：15 Percentile：45.53(Physics, Fluids & Plasmas)Design studies are shown on the National Centralized Tokamak facility. The machine design is carried out to investigate the capability for the flexibility in aspect ratio and shape controllability for the demonstration of the high-beta steady state operation with nation-wide collaboration, in parallel with ITER towards DEMO. Two designs are proposed and assessed with respect to the physics requirements such as confinement, stability, current drive, divertor, and energetic particle confinement. The operation range in the aspect ratio and the plasma shape is widely enhanced in consistent with the sufficient divertor pumping. Evaluations of the plasma performance towards the determination of machine design are presented.
Kiriyama, Hiromitsu; Yamakawa, Koichi; Kageyama, Nobuto*; Miyajima, Hirofumi*; Kan, Hirofumi*; Yoshida, Hidetsugu*; Nakatsuka, Masahiro*
Japanese Journal of Applied Physics, Part 1, 44(10), p.7464 - 7471, 2005/10
Times Cited Count：2 Percentile：9.29(Physics, Applied)no abstracts in English
Hazama, Osamu; Nakajima, Norihiro; Post, P.*; Wolf, K.*
Proceedings of 8th US National Congress on Computational Mechanics (USNCCM-8) (CD-ROM), 1 Pages, 2005/07
Computational science has always played an import role in nuclear engineering because it is quite difficult, if not impossible, to carry out experiments on the actual full-scale reactors in operation. We have been developing a numerical simulation infrastructure for carrying out numerical experiments on the virtual reactors constructed within computers. In order to understand the physical behavior of a reactor, interactions among various physial phenomena must be considered and understood. Therefore, a generic coupler has been developed to connect various software and hardware for the purposes of coupled simulations. Since this type of simulation requires large amount of computational resources, the coupler development is carried out on the ITBL GRID infrastructure. The development of this coupler and its applications to parallel and distributed coupled simulations with future development plans are reported.
Hazama, Osamu; Nakajima, Norihiro
Keisan Kogaku Koenkai Rombunshu, 10(1), p.259 - 260, 2005/05
It is impossible to carry out a controlled laboratory experiments on an operational full-scale power plant. Therefore, construction of a testbed to assess the safety of such systems by numerical means is believed to be meaningful. At CCSE/JAERI, a project to develop a numerical testbed to assess the safety of nuclear reactors have been begun. Simulations of such complex systems will inevitably require tremendous amount of computational resources. Therefore, the numerical testbed is constructed on the ITBL Grid middleware. A prototype of a generic software coupling interface was developed to couple various simulation software within the ITBL Grid environment to execute large-scale multi-disciplinary simulations on the testbed. This coupler and its application to some fluid-structure problems will be illustrated.
Yamada, Susumu; Imamura, Toshiyuki*; Machida, Masahiko; Arakawa, Chuichi*
Nihon Keisan Kogakkai Rombunshu, 7, p.243 - 252, 2005/05
no abstracts in English
Hazama, Osamu; Nakajima, Norihiro
Proceedings of 6th MpCCI User Forum, p.76 - 77, 2005/05
In order to accurately solve complex physical phenomena, interactions of various phenomena must be considered, which makes simulations multi-disciplinary. We have been developing a virtual nuclear reactor simulator on the ITBL Grid infrastructure in order to assess the safety of the nuclear reactors. This simulator system allows for numerical experiments on the full-scale and fully operational virtual nuclear reactors which is not possible in real-life experiments. In order to clarify various complex physical phenomena within the reactors, multi-disciplinary simulations, which are computationally demanding, are required. We have been developing a software to allow concurrent use of arbitrary combination of hardware and software to realize a multi-disciplinary simulation system on the ITBL. We have used STAMPI, developed by CCSE/JAERI, and MpCCI, developed by Fraunhofer SCAI, to construct the system. The system is now functional on the ITBL and will be introduced.
