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Watanabe, Tomoaki; Aizawa, Naoto*; Chiba, Go*; Tada, Kenichi; Yamamoto, Akio*
Proceedings of International Conference on Mathematics and Computational Methods Applied to Nuclear Science and Engineering (M&C 2025) (Internet), p.288 - 297, 2025/04
Currently, a major burnup calculation method for the nuclide composition of nuclear fuel conducts neutron transport calculations at each burnup step to account for changes in the neutron spectrum. While this method is highly accurate, the large computational cost of neutron transport calculations can be problematic. Therefore, a fast burnup calculation method based on neutron spectrum reconstruction with the proper orthogonal decomposition (POD) and regression model is investigated. In this method, dimensionality reduction by POD is applied to many neutron fluxes obtained from detailed burnup calculations for various input parameter sets, and regression models are constructed to connect the dimensionality-reduced neutron fluxes and parameters. By substituting arbitrary input parameters to the regression models, the neutron flux is reconstructed and the burnup calculation is performed. This method performs burnup calculations that consider changes in the neutron spectrum based on input conditions without neutron transport calculations. The present method was applied to a PWR UO
fuel pin cell model. The results show the nuclide inventory can be calculated with a prediction accuracy within a few percent. In addition, it is found that the calculation error is dominated by the regression models, which implies the further improvement of the regression models leads to improving the accuracy.
Watanabe, Tomoaki; Aizawa, Naoto*; Chiba, Go*; Tada, Kenichi; Fujita, Tatsuya*; Yamamoto, Akio*
Journal of Nuclear Science and Technology, 21 Pages, 2025/00
Times Cited Count：0 Percentile：0.00A fast burnup calculation method based on neutron spectrum reconstruction is proposed. The method employs a reduced-order model (ROM), constructed using proper orthogonal decomposition (POD) and regression models, to estimate neutron spectra experienced by fuel during burnup. The ROM is built from snapshot data generated through detailed burnup and neutron transport simulations under various conditions. During burnup calculations, the ROM is used to rapidly reconstruct neutron spectra at each burnup step. These reconstructed spectra are then used to compute one-group cross sections from multi-group effective cross sections derived using background cross sections. The proposed method significantly reduces computational time by avoiding repeated neutron transport simulations. Its performance is demonstrated using a PWR UO fuel pin model. Results show that, with the 6th-order POD, the method predicts nuclide inventories with an average error within 
5% compared to reference Monte Carlo calculations. Error analysis indicates that prediction accuracy is primarily limited by the regression models, rather than by the POD truncation or the multi-group cross section calculations.
Np and 
Am by accelerator-driven system at Kyoto University Critical AssemblyPyeon, C. H.*; Yamanaka, Masao*; Oizumi, Akito; Fukushima, Masahiro; Chiba, Go*; Watanabe, Kenichi*; Endo, Tomohiro*; Van Rooijen, W. G.*; Hashimoto, Kengo*; Sakon, Atsushi*; et al.
Journal of Nuclear Science and Technology, 56(8), p.684 - 689, 2019/08
Times Cited Count：12 Percentile：70.75(Nuclear Science & Technology)This study demonstrates, for the first time, the principle of nuclear transmutation of minor actinide (MA) by the accelerator-driven system (ADS) through the injection of high-energy neutrons into the subcritical core at the Kyoto University Critical Assembly. The main objective of the experiments is to confirm fission reactions of neptunium-237 (Np) and americium-241 (Am), and capture reactions of Np. Subcritical irradiation of Np and Am foils is conducted in a hard spectrum core with the use of the back-to-back fission chamber that obtains simultaneously two signals from specially installed test (Np or Am) and reference (uranium-235) foils. The first nuclear transmutation of Np and Am by ADS soundly implemented by combining the subcritical core and the 100 MeV proton accelerator, and the use of a lead-bismuth target, is conclusively demonstrated through the experimental results of fission and capture reaction events.
Aizawa, Kosuke; Fujita, Kaoru; Kamide, Hideki; Kasahara, Naoto*
Nuclear Technology, 189(2), p.111 - 121, 2015/02
Times Cited Count：0 Percentile：0.00(Nuclear Science & Technology)Selector-valve mechanism is adopted in the design of JSFR for its failed-fuel detection and location (FFDL) system. JSFR has only two FFDL units for 562 core fuel subassemblies to reduce construction cost by decreasing the reactor vessel diameter. Consequently, one SV-FFDL unit must handle about 300 subassemblies. In addition, JSFR adopts an upper internal structure (UIS) with a slit above the core. Sampling performance for the subassemblies under the UIS slit has been evaluated to be lower than those under the normal UIS position in the previous water experiments and numerical simulation. In this paper, the outline of FFDL system is shown, which can be applied to so large number of fuel subassemblies in a compact reactor vessel. Detection capability of the FFDL system was studied to achieve the design conditions. Operation modes and procedure of the FFDL system also investigated.
Aizawa, Kosuke; Fujita, Kaoru; Hirata, Shingo*; Kasahara, Naoto*
Nuclear Technology, 183(1), p.1 - 12, 2013/07
In the design of Japan Sodium-cooled Fast Reactor (JSFR), a selector-valve mechanism is adopted for its failed-fuel detection and location (FFDL) system. Since JSFR has only two FFDL units for about 600 fuel subassemblies, one FFDL unit must handle much larger number of subassemblies than in previous designs. In addition, during long plant life of 60 years, the wear length of the selector-valve will become longer than those of past reactors. Therefore, the endurance of the selector-valve becomes important. To demonstrate the manufacturability and endurance of the selector-valve, a full size mock-up was manufactured, and an endurance experiment of the mock-up model under high-temperature sodium were conducted. The cross-section observation, hardness measurement, and chemical assay results after the endurance experiment showed that the coating layer on the sliding surface still remains. Thus, the endurance of the JSFR selector-valve was demonstrated.
Aizawa, Kosuke; Oshima, Jun*; Kamide, Hideki; Kasahara, Naoto
Journal of Nuclear Science and Technology, 49(1), p.47 - 60, 2012/01
Times Cited Count：2 Percentile：16.49(Nuclear Science & Technology)A selector-valve type failed fuel detection and location (FFDL) system is applied to the JSFR design that has an upper internal structure (UIS) with a slit above the core and several sampling nozzles for the FFDL are set in the UIS around the slit to detect the fission product (FP) from the subassemblies below the slit. Therefore, mixing process in the UIS should be known and appropriate arrangement of the sampling nozzles in the UIS is needed. A water experiment using a 1/5-scle model was carried out. Experimental results showed that the sampling nozzles set in the UIS detected the FP simulant concentration within the criteria of FFDL signal detection. In addition, identification of the failed fuel subassembly under the UIS slit was achieved by means of comparing concentration profiles in the UIS. A numerical simulation using a CFD code was carried out. The simulation results showed that the simulation predicts the FP concentration distributions.
Aizawa, Kosuke; Oshima, Jun*; Kamide, Hideki; Kasahara, Naoto
Proceedings of International Conference on Fast Reactors and Related Fuel Cycles (FR 2009) (CD-ROM), 11 Pages, 2012/00
JSFR adopts a Selector-Valve mechanism for the failed fuel detection and location (FFDL) system. The Selector-Valve FFDL system identifies failed fuel subassemblies by sampling sodium from each fuel subassembly outlet and detecting fission product or delayed neutron. One of the JSFR design features is employing an upper internal structure (UIS) with a radial slit, in which an arm of fuel handling machine can move and access the fuel assemblies under the UIS. Thus, JSFR cannot place sampling nozzles right above the fuel subassemblies located under the slit. To overcome above diffculties, we have developed the sampling method for indentifying the failed fuel subassemblies located under the slit by numerical simulations and water experiments.
Aizawa, Kosuke; Fujita, Kaoru; Kamide, Hideki; Kasahara, Naoto
Proceedings of 2011 International Congress on Advances in Nuclear Power Plants (ICAPP '11) (CD-ROM), p.605 - 613, 2011/05
A conceptual design study of an advanced large-sized (1,500 MWe class) sodium-cooled fast reactor, JSFR, is in progress in the FaCT project in Japan. JSFR has adopted a selector-valve mechanism for a failed-fuel detection and location (FFDL) system. The selector-valve FFDL system identifies a failed fuel subassembly by sampling sodium from each fuel subassembly outlet and detecting fission product gas or delayed neutron precursors of fission products. One of the technologies which JSFR has adopted is an upper internal structure (UIS) with a radial slit. Because sampling nozzles cannot be set in the UIS slit, several sampling nozzles are installed around the slit so as to sample sodium from the failed fuel subassemblies under the UIS slit. In this study, a signal and noise detected by the delayed neutron detector have been calculated. On the basis of these results, appropriate operation patterns of the selector-valve FFDL system for JSFR have been constructed.
Aizawa, Kosuke; Fujita, Kaoru; Kamide, Hideki; Kasahara, Naoto
Nihon Kikai Gakkai Rombunshu, B, 77(776), p.982 - 986, 2011/04
A conceptual design study of Japan Sodium-cooled Fast Reactor (JSFR) is in progress as an issue of the "Fast Reactor Cycle Technology Development (FaCT)" project in Japan. JSFR adopts a Selector-Valve mechanism for a failed fuel detection and location (FFDL) system. The Selector-Valve FFDL system identifies failed fuel subassemblies by sampling sodium from each fuel subassembly outlet and detecting fission product. One of the JSFR design features is employing an upper internal structure (UIS) with a radial slit, in which an arm of fuel handling machine can move and access the fuel assemblies under the UIS. Thus, JSFR cannot place sampling nozzles right above the fuel subassemblies located under the slit. In this study, appropriate sampling method for indentifying under-slit failed fuel subassemblies has been developed by water experiments.
Kamide, Hideki; Aizawa, Kosuke; Oshima, Jun*; Nakayama, Okatsu*; Kasahara, Naoto
Journal of Nuclear Science and Technology, 47(9), p.810 - 819, 2010/09
Times Cited Count：3 Percentile：22.64(Nuclear Science & Technology)Development of advanced loop type sodium cooled fast reactor is under going. An upper internal structure (UIS) has a radial slit to reduce the reactor vessel diameter. This UIS slit allows a high velocity from the core fuel subassemblies and influences the gas entrainment in the reactor vessel and also the delayed neutron precursor sampling for a failed fuel detection and location system. Then flow visualization and velocity measurements were carried out in an 1/10 scale water test model. The velocity measurement using particle image velocimetry showed that velocity in the slit region was accelerated at the heights of the UIS horizontal plates and kept higher value at the middle height of the upper plenum. Numerical simulation using a commercial CFD code was also carried out for this complex geometry of UIS to know adequate simulation method. The comparisons of velocity profiles in the UIS between the experiment and analysis showed good agreements.
Aizawa, Kosuke; Fujita, Kaoru; Kamide, Hideki; Kasahara, Naoto
Dai-15-Kai Doryoku, Enerugi Gijutsu Shimpojiumu Koen Rombunshu, p.229 - 230, 2010/06
A conceptual design study of Japan Sodium-cooled Fast Reactor (JSFR) is in progress as an issue of the "Fast Reactor Cycle Technology Development (FaCT)" project in Japan. JSFR adopts a selector-valve mechanism for the Failed Fuel Detection and Location (FFDL) system. The selector-valve FFDL system identifies failed fuel subassemblies by sampling sodium from each fuel subassembly outlet and detecting fission product. One of the JSFR design features is employing an Upper Internal Structure (UIS) with a radial slit, in which an arm of fuel handling machine can move and access the fuel assemblies under the UIS. Thus, JSFR cannot place sampling nozzles right above the fuel subassemblies located under the slit. In this study, the sampling method for identifying under-slit failed fuel subassemblies has been demonstrated by water experiments.
Aizawa, Kosuke; Fujita, Kaoru; Hirata, Shingo; Kasahara, Naoto
Proceedings of 2010 International Congress on Advances in Nuclear Power Plants (ICAPP '10) (CD-ROM), p.645 - 652, 2010/06
A conceptual design study of an advanced large-sized (1500MWe class) sodium-cooled fast reactor (named JSFR) has progressed in the FaCT project in Japan. JSFR adopts a selector-valve mechanism for the failed fuel detection and location (FFDL) system. The drive shaft rotates and moves vertically in order to select the channel. And, the drive shaft is in contact with the selector-valve drum by spring load. Thus, a mechanical wear could occur between the drive shaft and the drum of the selector-valve FFDL system. There is concern about manufacturing capability and endurance of the JSFR selector-valve. To demonstrate manufacturing capability and endurance of the JSFR selector-valve, a mock-up was manufactured and an endurance experiment under high temperature sodium has been conducted.
Kamide, Hideki; Aizawa, Kosuke; Oshima, Jun*; Nakayama, Okatsu*; Kasahara, Naoto
Proceedings of 6th Japan-Korea Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS-6) (USB Flash Drive), 8 Pages, 2008/11
Development of advanced loop type sodium cooled fast reactor is under going. An upper internal structure (UIS) has a radial slit to reduce the reactor vessel diameter. This UIS slit allows a high velocity from the core fuel subassemblies and influences the gas entrainment in the reactor vessel and also the delayed neutron precursor sampling for a failed fuel detection and location system. Then flow visualization and velocity measurements were carried out in an 1/10 scale water test model. The velocity measurement using particle image velocimetry showed that velocity in the slit region was accelerated at the heights of the UIS horizontal plates and kept higher value at the middle height of the upper plenum. Numerical simulation using a commercial CFD code was also carried out for this complex geometry of UIS to know adequate simulation method. The comparisons of velocity profiles in the UIS between the experiment and analysis showed good agreements.
Kawabata, Kosuke*; Aizawa, Naoto*; Sugawara, Takanori
no journal, ,
We performed the neutronics design of accelerator-driven system (ADS) with 100 MW thermal power for various RI production and material irradiation. Through the analysis with the use of the Serpent2 code, core concepts which satisfy the limit values were presented.
Nakamura, Kensuke*; Aizawa, Koki*; Asamori, Koichi; Oshiman, Naoto*; Shiozaki, Ichiro*; The 2001 Research Group for Crustal Resistivity structure*
no journal, ,
We show the resistivity structure around the focal region of the 2000 Western Tottori Earthquake (M7.3). The purpose of this study is to investigate the relationship between the rupture of the mainshock and the resistivity structure, which was not discussed in the previous study. By using the broad-band MT data, Umeda et al. (2011) imaged a deep conductive body in the middle crust to the upper mantle on the southwestern side of the mainshock rupture fault. However, they did not investigate the spatial relationship between the resistivity structure and the slip distribution. Therefore, in this re-analysis, we have spatial attention to the shape and uniqueness of the conductors. In addition to the previous broad-band MT data, we use broad-band MT data at 12 sites obtained by Universities (The 2001 Research Group for Crustal Resistivity structure, Japan, 2001). We use full components of the impedance tensor and geomagnetic transfer functions to image preliminary 3-D resistivity structure, and investigate its relationship to the slip distribution of the mainshock and also occurrence of the aftershocks.
Ushio, Tadashi*; Aizawa, Naoto*; Fujita, Tatsuya; Gunji, Satoshi
no journal, ,
The reactor physics road map is and has to remain "the guide for reactor physics engineers/researchers in considering future directions of technology and research developments," thus the periodical rolling by reactor physics engineers/researchers is necessary. In consideration of the fact that five years have already passed since the current 2017 version (RM2017, October 2017) was developed, and the environment surrounding nuclear energy has significantly changed such as the developments of GX (Green Transformation) strategy and Carbon-Neutrality by 2050, a new 2024 version (RM2024) was developed by revising RM2017 through the review of current items and descriptions. In the planning lecture by the reactor physics division, the details of this rolling work are introduced, and the expectations for the road map, the requirements for ideal road map, the desirable items, etc. are discussed by an exchange of opinions with reactor physics engineers/researchers.
Nakamura, Kensuke*; Aizawa, Koki*; Asamori, Koichi; Oshiman, Naoto*; Shiozaki, Ichiro*; The 2001 Research Group for Crustal Resistivity structure*
no journal, ,
Nakajima, Kenji; Nakamura, Mitsutaka; Inamura, Yasuhiro; Kajimoto, Ryoichi; Wakimoto, Shuichi; Osakabe, Toyotaka; Metoki, Naoto; Ito, Shinichi*; Sato, Taku*; Kakurai, Kazuhisa; et al.
no journal, ,
no abstracts in English
Watanabe, Tomoaki; Aizawa, Naoto*; Chiba, Go*; Tada, Kenichi; Fujita, Tatsuya*; Yamamoto, Akio*
no journal, ,
We currently propose a fast burnup calculation method using a low-dimensional neutron spectrum prediction model based on Proper Orthogonal Decomposition (POD). In previous studies, the impact of prediction errors in the neutron spectrum on nuclide inventory estimates has been considered; however, the multi-group effective cross-section calculation used to derive energy-averaged cross sections from the neutron spectrum had not yet been addressed. In this study, we incorporated the multi-group effective cross-section calculation into the proposed method and evaluated the overall computational accuracy. As a result, it was confirmed that the impact of the multi-group effective cross-section calculation on the accuracy of nuclide inventory is sufficiently small. Furthermore, a comparative analysis was conducted using both 172-group and 361-group energy structures, and it was found that employing the finer 361-group structure improves the calculation accuracy for several fission product nuclides.
Nakajima, Kenji; Kawamura, Seiko; Kajimoto, Ryoichi; Inamura, Yasuhiro; Takahashi, Nobuaki; Osakabe, Toyotaka; Wakimoto, Shuichi; Nakamura, Mitsutaka; Ito, Shinichi*; Aizawa, Kazuya; et al.
no journal, ,
no abstracts in English
