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Ota, Akira*; Ito, Sho*; Sonobe, Hideaki*; Ino, Susumu*; Choi, B.; Nishida, Akemi; Shiomi, Tadahiko
Nuclear Engineering and Design, 444, p.114403_1 - 114403_7, 2025/12
Times Cited Count：0 Percentile：0.00no abstracts in English
Ichihara, Yoshitaka*; Nakamura, Naohiro*; Nabeshima, Kunihiko*; Choi, B.; Nishida, Akemi
Nuclear Engineering and Design, 441, p.114160_1 - 114160_10, 2025/09
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)This paper evaluates the applicability of equivalent linear analysis of reinforced concrete model, which uses frequency-independent complex damping with a small computational load, to the seismic design of nuclear power plant reactor buildings. To this end, a three-dimensional finite element method analysis of the soil-structure interaction focusing on nonlinear and equivalent linear seismic behavior of the building embedded in an ideally uniform soil condition was performed for the Kashiwazaki-Kariwa Nuclear Power Plant Unit 7 reactor building. The equivalent linear analysis results correlated well with the nonlinear analysis results of the shear strain, acceleration, displacement, and acceleration response spectrum, demonstrating the effectiveness of the equivalent linear analysis method. Moreover, the equivalent linear analysis results were more conservative than those of nonlinear analysis using the material constitutive law in evaluating the shear strain of the external wall of the reactor building. From this result, equivalent linear analysis method tended to obtain a lower building stiffness than nonlinear analysis under the analysis conditions used in this paper.
Nishida, Akemi; Choi, B.; Kang, Z.; Shiomi, Tadahiko; Iigaki, Kazuhiko; Yamakawa, Koki*
Transactions of the 28th International Conference on Structural Mechanics in Reactor Technology (SMiRT28) (Internet), 10 Pages, 2025/08
Our research and development are aimed at improving the accuracy of the three-dimensional seismic analysis of nuclear buildings to better understand their three-dimensional seismic behavior in response to enhanced regulatory requirements on impact assessment against external events such as earthquakes. In 2019, we constructed a large-scale observation system for the High Temperature Engineering Test Reactor (HTTR) building of the Japan Atomic Energy Agency (JAEA) in collaboration with the Nuclear Regulation Authority (NRA) and JAEA. Since then, we also conducted several excitation tests by the ACROSS system and obtained observation record at many accelerometers using the observation system. These records are important since the excitation source is clearly defined unlike earthquake's uncertain transmission pathway. In this paper, we focus mainly on the vibration characteristics of the entire building and report on these observation records and the characteristics, such as the dominant frequencies and corresponding three-dimensional deformation modes.
Yamakawa, Koki*; Hiramatsu, Masako*; Moritani, Hiroshi*; Iiba, Masanori*; Nishida, Akemi; Shiomi, Tadahiko; Choi, B.; Iigaki, Kazuhiko
Transactions of the 28th International Conference on Structural Mechanics in Reactor Technology (SMiRT28) (Internet), 9 Pages, 2025/08
To understand the three-dimensional seismic behavior of nuclear buildings, the Nuclear Regulation Authority (NRA) and the Japan Atomic Energy Agency (JAEA) have been conducting research and development aimed at improving the accuracy of three-dimensional seismic analysis methods for nuclear buildings. A large-scale observation system was constructed in the High Temperature engineering Test Reactor (HTTR) building of JAEA, enabling seismic observation and artificial wave excitation. Using this system, vibration characteristics of the HTTR building have been analyzed based on both seismic observation records and analyses using a three-dimensional seismic analysis model of the HTTR building. This paper reports on the vibration characteristics of the HTTR building obtained from the analysis of seismic observation records, as well as on the improvements made to the three-dimensional finite element model and the results of simulation analyses using artificial waves. In particular, this paper presents the results of an analysis of the Fourier spectral ratio at the first floor of the HTTR building based on seismic records, and discusses the dominant frequencies and acceleration modes of the superstructure.
Choi, B.; Nishida, Akemi; Tsutsumi, Hideaki*; Takada, Tsuyoshi
Transactions of the 28th International Conference on Structural Mechanics in Reactor Technology (SMiRT28) (Internet), 10 Pages, 2025/08
One of the key lessons learned from the Fukushima Daiichi Nuclear Power Plant accident is the necessity of developing a probabilistic risk assessment (PRA) method that considers multiple external hazards (multi-hazards), such as earthquakes and tsunamis. In this study, we organized classification concepts for multi-hazards that could lead to significant disasters. A classification method for multi-hazard scenarios was developed based on causal relationships (dependent or independent) and temporal relationships (simultaneous or time-lagged occurrence). Furthermore, we examined modeling approaches for multi-hazard scenarios using the developed classification method. The modeling considered elements such as hazard curves, hazard intensity, hazard frequency, time, and event duration, and these were defined in terms of conditional probability density functions. This paper reports application examples of multi-hazard evaluation under hypothetical site and analysis conditions, focusing on representative scenarios such as earthquake-tornado and earthquake-tsunami combinations, based on the multi-hazard classification method developed in previous studies.
Kang, Z.; Okuda, Yukihiko; Nishida, Akemi; Tsubota, Haruji; Ito, Masaharu
Mechanical Engineering Journal (Internet), 12(4), p.24-00450_1 - 24-00450_12, 2025/03
no abstracts in English
Takito, Kiyotaka; Okuda, Yukihiko; Nishida, Akemi; Li, Y.
Journal of Pressure Vessel Technology, 146(6), p.061301_1 - 061301_12, 2024/12
Times Cited Count：0 Percentile：0.00(Engineering, Mechanical)Kang, Z.; Okuda, Yukihiko; Nishida, Akemi; Tsubota, Haruji; Ito, Masaharu; Li, Y.
Proceedings of 31st International Conference on Nuclear Engineering (ICONE31) (Internet), 9 Pages, 2024/11
Most studies conducted till now on local damage of reinforced concrete (RC) slab structures subjected to missile impact are about normal impact, while few research related to oblique impact can be found. The objective of this study is to carry out impact tests under different impact conditions including oblique impacts, to confirm the different impact behaviors of the RC slab structure, to develop an analysis method by investigating the test results and analytical conditions, and to validate the analysis method through comparison with the test results. This study focuses on the effect of the stiffness of the supports for oblique impact on the reaction forces of RC slab. Until now, static loading tests were conducted to confirm the stiffnesses of the supporting parts that supported the RC specimen during oblique impact tests. Based on the obtained load-displacement relationships, and so on, the stiffnesses of the supporting parts are estimated.
Choi, B.; Nishida, Akemi; Tsutsumi, Hideaki*; Takada, Tsuyoshi
Proceedings of Probabilistic Safety Assessment and Management & Asian Symposium on Risk Assessment and Management (PSAM17 & ASRAM2024) (Internet), 8 Pages, 2024/10
The Fukushima Daiichi Nuclear Power Plant accident highlighted the importance of developing safety assessment methods that consider multihazard events involving numerous simultaneously occurring events such as earthquakes (shaking) and tsunamis (submersion). When addressing such multihazard events, traditional methods often focus on assessing the load combinations of general structures in their structural designs and adopt simple selection criteria. However, these methods fall short when evaluating, countering, and screening external events, such as earthquakes, tsunamis, strong winds, and concentrated heavy rainfall, that occur simultaneously or in a chain. To address this, we reviewed existing literature on multihazard assessment methods, focusing particularly on scenarios involving earthquake and tsunami events. Based on concepts and basic theories, we examined various methods for addressing multihazard scenarios and classified their characteristics. Specifically, several multihazard scenarios were surveyed, and the relationships between multiple hazards were organized. In addition, common causes leading to combined events, their mutual influences, and potential cascading effects were analyzed.
Takito, Kiyotaka; Okuda, Yukihiko; Nishida, Akemi; Li, Y.
Proceedings of the ASME 2024 Pressure Vessels & Piping Conference (PVP 2024) (Internet), 9 Pages, 2024/07
In probabilistic risk assessment against earthquakes (seismic PRA), one of the important issues is the development of a realistic response analysis method for evaluating the fragility of equipment and piping systems subject to input ground motions exceeding design assumption. Particularly, piping systems have complex plant-specific three-dimensional geometries. The arrangement and rigidity of piping support structures have significant impact on the response characteristics of the entire piping system. Therefore, it is necessary to develop a seismic response analysis method for piping systems, including piping support structures. To this end, the authors have been working on the development of elasto-plastic analysis method for piping support structures in order to establish a realistic response analysis method for piping systems including piping support structures. In this study, parametric studies on important analytical parameters were conducted to understand the influence of the analytical parameters on the deformation in the elasto-plastic analysis of piping support structures. At first, a three-dimensional finite element analysis model was created for cyclic loading tests of a gate type piping support structure assuming large deformations. Using the model, parametric studies were conducted for analysis parameters such as yield stress, secondary stiffness and element size. As the result, the influences of the analysis parameters on the analysis results were quantitatively clarified, which provided insight into the methodology for setting appropriate analysis parameters on elasto-plastic analysis for piping support structures.
Okuda, Yukihiko; Takito, Kiyotaka; Nishida, Akemi; Li, Y.
Mechanical Engineering Journal (Internet), 11(2), p.23-00405_1 - 23-00405_12, 2024/04
After the Great East Japan earthquake and the accident at the TEPCO's Fukushima Daiichi Nuclear Power Stations in March 2011, the regulation for nuclear power plants (NPPs) has been enhanced to take countermeasures against beyond-design-basis events. To improve the seismic safety of nuclear facilities against earthquakes that exceed the design input ground motion, the importance of seismic probabilistic risk assessment (PRA) has drawn much attention. It is essential to evaluate the realistic seismic response of the equipment and piping in NPPs for fragility assessment in seismic PRA. In particular, since piping systems have plant-specific complex route geometries, it is known that the arrangement and stiffness of piping support structures have a significant impact on seismic response characteristics of the entire piping system. To construct a realistic seismic response analysis method for excessive input ground motion exceeding the elastic response, it is desired to develop an elastic-plastic response analysis method that can estimate the realistic response of piping systems including pipe support structures. In this study, the applicability of the method is confirmed by the simulation analysis of the elasto-plastic response for the piping support structure loading test previously reported. Moreover, based on the good correlation between the ductility factor and the damage status obtained from the test results and simulation analysis results, it is shown that the ductility factor is effective as a damage evaluation index for piping support structures.
Choi, B.; Nishida, Akemi; Kawata, Manabu; Shiomi, Tadahiko; Li, Y.
JAEA-Research 2024-001, 206 Pages, 2024/03
JAEA-Research-2024-001.pdf:9.12MB
In the assessment of seismic safety and the design of building structures in nuclear facilities, lumped mass models have been used as standard methods. Recent advances in computer capabilities allow the use of three-dimensional finite element (3D FE) models to account for the 3D behavior of buildings, material nonlinearity, and the nonlinear soil-structure interaction effect. While 3D analysis method has many advantages, it is necessary to ensure its reliability as a new approach. The International Atomic Energy Agency performed an international benchmark study using the 3D FE analysis model for reactor building of Unit 7 at TEPCO's Kashiwazaki-Kariwa Nuclear Power Station based on recordings from the Niigataken Chuetsu-oki Earthquake in 2007. Multiple organizations from different countries participated in this study and the variation in their analytical results was significant, indicating an urgent need to improve the reliability of the analytical results by standardization of the analytical methods using 3D FE models. Additionally, it has been pointed out that it is necessary to understand the 3D behavior in the seismic fragility assessment of buildings and equipment, using realistic seismic response analysis method based on 3D FE models. In view of these considerations, a guideline for the seismic response analysis method using a 3D FE model was developed by incorporating the latest knowledge and findings in this area. The purpose of the guideline is to improve the reliability of the seismic response analysis method using 3D FE model of reactor buildings. The guideline consists of a main body, commentaries, and appendixes. The standard procedures, recommendations, key points to note, and technological bases for conducting seismic response analysis on reactor buildings using 3D FE models are provided in the guideline. In addition, the guideline will be revised reflecting the latest knowledge.
Nishida, Akemi
Kenchiku Gijutsu, (890), p.86 - 89, 2024/03
no abstracts in English
Muramatsu, Ken; Kubo, Kotaro; Choi, B.; Nishida, Akemi; Takada, Tsuyoshi
Transactions of the 27th International Conference on Structural Mechanics in Reactor Technology (SMiRT 27) (Internet), 10 Pages, 2024/03
no abstracts in English
Matsukawa, Keisuke*; Satoda, Akira*; Nishida, Akemi; Guo, Z. H.*
Transactions of the 27th International Conference on Structural Mechanics in Reactor Technology (SMiRT 27) (Internet), 10 Pages, 2024/03
no abstracts in English
Choi, B.; Nishida, Akemi; Takito, Kiyotaka; Tsutsumi, Hideaki*; Takada, Tsuyoshi
Transactions of the 27th International Conference on Structural Mechanics in Reactor Technology (SMiRT 27) (Internet), 10 Pages, 2024/03
no abstracts in English
Kang, Z.; Okuda, Yukihiko; Nishida, Akemi; Tsubota, Haruji; Li, Y.
Transactions of the 27th International Conference on Structural Mechanics in Reactor Technology (SMiRT 27) (Internet), 10 Pages, 2024/03
Most studies conducted till now on local damage of reinforced concrete (RC) slab structures subjected to projectile impact are about normal impact, while few research related to oblique impact can be found. The objective of this study is to carry out impact tests under different impact conditions including oblique impacts, to confirm the different impact behaviors of the RC slab structure, to develop an analysis method by investigating the test results and analytical conditions, and to validate the analysis method through comparison with the test results. This study focuses on the scabbing damage which is one of the local damage modes of RC slab. Based on oblique impact test results due to soft projectile with hemispherical nose shape, we investigate the relationship between the criterion related to the concrete fracture and the occurrence of scabbing damage.
Nishida, Akemi; Kawata, Manabu; Choi, B.; Kunitomo, Takahiro; Shiomi, Tadahiko; Iigaki, Kazuhiko; Yamakawa, Koki*
Transactions of the 27th International Conference on Structural Mechanics in Reactor Technology (SMiRT 27) (Internet), 10 Pages, 2024/03
no abstracts in English
Ito, Sho*; Ota, Akira*; Sonobe, Hideaki*; Ino, Susumu*; Choi, B.; Nishida, Akemi; Shiomi, Tadahiko
Transactions of the 27th International Conference on Structural Mechanics in Reactor Technology (SMiRT 27) (Internet), 10 Pages, 2024/03
no abstracts in English
Okuda, Yukihiko; Kang, Z.; Nishida, Akemi; Tsubota, Haruji; Li, Y.
Transactions of the 27th International Conference on Structural Mechanics in Reactor Technology (SMiRT 27) (Internet), 10 Pages, 2024/03
The outer walls of nuclear facility buildings consist of reinforced concrete (RC) panels. When a projectile collides with a nuclear facility building, local damages such as penetration, scabbing, and perforation can occur in the RC panels. Numerical simulation using finite element analysis (FEA) is generally employed to assess these damage conditions. However, the impact analysis by FEA modelled with continuum elements is difficult to address phenomena such as scattering fragments of concrete because the elements deletion method for large deformation is used to prevent interruption of numerical calculations. Recently, a numerical method known as Smooth Particles Hydrodynamics (SPH), one of the particle methods, has been employed to address discontinuous phenomena. In this paper, we focus on the scabbing damages to RC panels and report on the findings obtained through the validation of the numerical analysis using the SPH method.
