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Journal Articles

Study on criticality safety control of fuel debris for validation of methodology applied to the safety regulation

Suyama, Kenya; Ueki, Taro; Gunji, Satoshi; Watanabe, Tomoaki; Araki, Shohei; Fukuda, Kodai; Yamane, Yuichi; Izawa, Kazuhiko; Nagaya, Yasunobu; Kikuchi, Takeo; et al.

Proceedings of 12th International Conference on Nuclear Criticality Safety (ICNC2023) (Internet), 6 Pages, 2023/10

To remove and store safely the fuel debris generated by the severe accident of the Fukushima Daiichi Nuclear Power Station in 2011 is one of the most important and challenging topics for decommissioning of the damaged reactors in Fukushima. To validate the adopted method for the evaluation of criticality safety control of the fuel debris through comparison with the experimental data obtained by the criticality experiments, the Nuclear Regulation Authority (NRA) of Japan funds a research and development project which was entrusted to the Nuclear Safety Research Center (NSRC) of Japan Atomic Energy Agency (JAEA) from 2014. In this project, JAEA has been conducting such activities as i) comprehensive computation of the criticality characteristics of the fuel debris and making database (criticality map of the fuel debris), ii) development of new continuous energy Monte Carlo code, iii) evaluation of criticality accident and iv) modification of the critical assembly STACY for the experiments for validation of criticality safety control methodology. After the last ICNC2019, the project has the substantial progress in the modification of STACY which will start officially operation from May 2024 and the development of the Monte Carlo Code "Solomon" suitable for the criticality calculation for materials having spatially random distribution complies with the power spectrum. We present the whole picture of this research and development project and status of each technical topics in the session.

Journal Articles

Application of quasi-Monte Carlo and importance sampling to Monte Carlo-based fault tree quantification for seismic probabilistic risk assessment of nuclear power plants

Kubo, Kotaro; Tanaka, Yoichi; Hakuta, Yuto*; Arake, Daisuke*; Uchiyama, Tomoaki*; Muramatsu, Ken

Mechanical Engineering Journal (Internet), 10(4), p.23-00051_1 - 23-00051_17, 2023/08

The significance of probabilistic risk assessments (PRAs) of nuclear power plants against external events was re-recognized after the Fukushima Daiichi Nuclear Power Plant accident. Regarding the seismic PRA, handling correlated failures of systems, components, and structures (SSCs) is very important because this type of failure negatively affects the redundancy of accident mitigation systems. The Japan Atomic Energy Research Institute initially developed a fault tree quantification methodology named the direct quantification of fault tree using Monte Carlo simulation (DQFM) to handle SSCs' correlated failures in detail and realistically. This methodology allows quantifying the top event occurrence probability by considering correlated uncertainties related to seismic responses and capacities with Monte Carlo sampling. The usefulness of DQFM has already been demonstrated. However, improving its computational efficiency would allow risk analysts to perform several analyses. Therefore, we applied quasi-Monte Carlo and importance sampling to the DQFM calculation of simplified seismic PRA and examined their effects. Specifically, the conditional core damage probability of a hypothetical pressurized water reactor was analyzed with some assumptions. Applying the quasi-Monte Carlo sampling accelerates the convergence of results at intermediate and high ground motion levels by an order of magnitude over Monte Carlo sampling. The application of importance sampling allows us to obtain a statistically significant result at a low ground motion level, which cannot be obtained through Monte Carlo and quasi-Monte Carlo sampling. These results indicate that these applications provide a notable acceleration of computation and raise the potential for the practical use of DQFM in risk-informed decision-making.

Journal Articles

A Scoping study on the use of direct quantification of fault tree using Monte Carlo simulation in seismic probabilistic risk assessments

Kubo, Kotaro; Fujiwara, Keita*; Tanaka, Yoichi; Hakuta, Yuto*; Arake, Daisuke*; Uchiyama, Tomoaki*; Muramatsu, Ken*

Proceedings of 29th International Conference on Nuclear Engineering (ICONE 29) (Internet), 8 Pages, 2022/08

After the Fukushima Daiichi Nuclear Power Plant accident, the importance of conducting probabilistic risk assessments (PRAs) of external events, especially seismic activities and tsunamis, was recognized. The Japan Atomic Energy Agency has been developing a computational methodology for seismic PRA, called the direct quantification of fault tree using Monte Carlo simulation (DQFM). When appropriate correlation matrices are available for seismic responses and capacities of components, the DQFM makes it possible to consider the effect of correlated failures of components connected through AND and/or OR gates in fault trees, which is practically difficult when methods using analytical solutions or multidimensional numerical integrations are used to obtain minimal cut set probabilities. The usefulness of DQFM has already been demonstrated. Nevertheless, a reduction of the computational time of DQFM would allow the large number of analyses required in PRAs conducted by regulators and/or operators. We; therefore, performed scoping calculations using three different approaches, namely quasi-Monte Carlo sampling, importance sampling, and parallel computing, to improve calculation efficiency. Quasi-Monte Carlo sampling, importance sampling, and parallel computing were applied when calculating the conditional core damage probability of a simplified PRA model of a pressurized water reactor, using the DQFM method. The results indicated that the quasi-Monte Carlo sampling works well at assumed medium and high ground motion levels, importance sampling is suitable for assumed low ground motion level, and that parallel computing enables practical uncertainty and importance analysis. The combined implementation of these improvements in a PRA code is expected to provide a significant acceleration of computation and offers the prospect of practical use of DQFM in risk-informed decision-making.

Journal Articles

Criticality characteristics of fuel debris mixed by fuels with different burnups based on fuel loading pattern

Watanabe, Tomoaki; Okubo, Kiyoshi*; Araki, Shohei; Tonoike, Kotaro

Proceedings of 11th International Conference on Nuclear Criticality Safety (ICNC 2019) (Internet), 8 Pages, 2019/09

Journal Articles

The Two-step nucleation of G-phase in ferrite

Matsukawa, Yoshitaka*; Takeuchi, Tomoaki; Kakubo, Yuta*; Suzudo, Tomoaki; Watanabe, Hideo*; Abe, Hiroaki*; Toyama, Takeshi*; Nagai, Yasuyoshi*

Acta Materialia, 116, p.104 - 113, 2016/09

 Times Cited Count:67 Percentile:95.7(Materials Science, Multidisciplinary)

Atom probe tomography (APT) and TEM were combined for identifying the stage at which solute clusters transform into compounds crystallographically distinct from the matrix, in the precipitation of the G-phase (Ni$$_{16}$$Si$$_{7}$$Mn$$_{6}$$) from ferrite solid solution subjected to isothermal annealing at 673 K. Based on a systematic analysis of solute clusters as a function of annealing time, the nucleation of the G-phase was found to occur via a two-step process. Moreover, the structural change was found to occur via another two-step process. There was a time lag between the end of cluster growth to become a critical size and the start of the structural change. During the incubation period solute enrichment occurred inside the clusters without further size growth, indicating that the nucleation of the G-phase occurs at the critical size with a critical composition. Judging from the results of APT, TEM and the simulation of electron diffraction patterns, the critical composition was estimated to be Ni$$_{16}$$Si$$_{3.5}$$(Fe,Cr)$$_{3.5}$$Mn$$_{6}$$.

Journal Articles

Effects of thermal aging on microstructure and hardness of stainless steel weld-overlay claddings of nuclear reactor pressure vessels

Takeuchi, Tomoaki; Kakubo, Yuta*; Matsukawa, Yoshitaka*; Nozawa, Yasuko*; Toyama, Takeshi*; Nagai, Yasuyoshi*; Nishiyama, Yutaka; Katsuyama, Jinya; Yamaguchi, Yoshihito; Onizawa, Kunio; et al.

Journal of Nuclear Materials, 452(1-3), p.235 - 240, 2014/09

 Times Cited Count:37 Percentile:95.26(Materials Science, Multidisciplinary)

Microstructures and hardness of stainless steel weld overlay cladding of reactor pressure vessels subjected to the thermal aging at 400 $$^{circ}$$C for 100-10,000 h were investigated using atom probe tomography and nanoindentation technique. The Cr concentration fluctuation in the $$delta$$-ferrite phase caused by spinodal decomposition rapidly progressed by the 100 h aging while NiSiMn clusters increased in number density at 2,000 h and coarsened at 10,000 h. The hardness of the $$delta$$-ferrite phase also rapidly increased at the short aging time. The Cr concentration fluctuation and the hardness were in good correlation with the degree of the Cr concentration fluctuation rather than the formation of the NiSiMn clusters. These results strongly suggested that the dominant factor of the hardening of the $$delta$$-ferrite phase by the thermal aging was Cr spinodal decomposition.

Journal Articles

Effects of neutron irradiation on microstructures and hardness of stainless steel weld-overlay cladding of nuclear reactor pressure vessels

Takeuchi, Tomoaki; Kakubo, Yuta*; Matsukawa, Yoshitaka*; Nozawa, Yasuko*; Toyama, Takeshi*; Nagai, Yasuyoshi*; Nishiyama, Yutaka; Katsuyama, Jinya; Yamaguchi, Yoshihito; Onizawa, Kunio

Journal of Nuclear Materials, 449(1-3), p.273 - 276, 2014/06

 Times Cited Count:18 Percentile:81.73(Materials Science, Multidisciplinary)

Microstructural changes and hardness of stainless steel weld overlay cladding of reactor pressure vessels subjected to the neutron irradiation with a dose of 7.2 $$times$$ 10$$^{19}$$n cm$$^{-2}$$ (E $$>$$ 1 MeV) and a flux of 1.1 $$times$$ 10$$^{13}$$n cm$$^{-2}$$ s$$^{-1}$$ at 290$$^{circ}$$C were investigated by atom probe tomography and with nanoindentation technique. In order to isolate the effect of the irradiation, we compared the results of the measurements of the irradiated sample with that of the aged one at 300$$^{circ}$$C for the time equivalent to the irradiation. The Cr concentration fluctuation was enhanced in the $$delta$$-ferrite phase of the irradiated sample. In addition, the enhancement of the concentration fluctuation of Si, which was not observed in the aged sample, was observed. The hardening at the $$delta$$-ferrite phase was occurred by both the irradiation and the aging. However, the former was more than that expected from the Cr concentration fluctuation, which suggested that the Si concentration fluctuation and irradiation-induced defects were possible origins of the additional hardening.

Journal Articles

RBS study of disordering of Fe$$_{3-x}$$Mn$$_{x}$$Si/Ge(111) heteroepitaxial interfaces

Noguchi, Masaya*; Hirata, Tomoaki*; Kawakubo, Yuki*; Narumi, Kazumasa; Sakai, Seiji; Maeda, Yoshihito

Physica Status Solidi (C), 10(12), p.1732 - 1734, 2013/12

 Times Cited Count:0 Percentile:0.01

Journal Articles

Ion beam analysis of quaternary Heusler alloy Co$$_{2}$$(Mn$$_{1-x}$$Fe$$_{x}$$)Si(111) epitaxially grown on Ge(111)

Kawakubo, Yuki*; Noguchi, Masaya*; Hirata, Tomoaki*; Narumi, Kazumasa; Sakai, Seiji; Yamada, Shinya*; Hamaya, Kohei*; Miyao, Masanobu*; Maeda, Yoshihito

Physica Status Solidi (C), 10(12), p.1828 - 1831, 2013/12

 Times Cited Count:0 Percentile:0.01

Journal Articles

Effect of neutron irradiation on the microstructure of the stainless steel electroslag weld overlay cladding of nuclear reactor pressure vessels

Takeuchi, Tomoaki; Kakubo, Yuta*; Matsukawa, Yoshitaka*; Nozawa, Yasuko*; Nagai, Yasuyoshi*; Nishiyama, Yutaka; Katsuyama, Jinya; Onizawa, Kunio; Suzuki, Masahide

Journal of Nuclear Materials, 443(1-3), p.266 - 273, 2013/11

 Times Cited Count:16 Percentile:76.81(Materials Science, Multidisciplinary)

Investigation on irradiation effects of weld-overlay claddings is necessary for safety assessment of reactor pressure vessels. We investigated microstructural changes in the cladding, which was composed of about 90% austenite and 10% $$delta$$-ferrite phases, subjected to the neutron irradiation to 7.2$$times$$10$$^{19}$$ n/cm$$^{2}$$ at 290$$^{circ}$$C, by 3D atom probe tomography technique. In the ferrite phase, the amplitude of the Cr and Si concentration fluctuation was increased by the irradiation and Ni and Mn concentration fluctuations were newly occurred. In the austenite phase, $$gamma$$'(Ni$$_{3}$$Si) -like clusters were formed. In contrast, the results of our previous work on the cladding subjected to thermal aging showed the amplitude of the Cr fluctuation was significantly increased and G (Ni-Si-Mn) phase was formed in the ferrite phase. Moreover, no changes were observed in the austenite by the aging.

Journal Articles

Present status of hydrogen production and the ammonia production by the thermochemical cycle; Introduction of IS cycle and ISN cycle

Kameyama, Hideo*; Sakurai, Makoto*; Masuda, Akiyuki*; Fukui, Tomoaki*; Onuki, Kaoru; Kubo, Shinji; Imai, Yoshiyuki

Suiso Enerugi Shisutemu, 37(1), p.3 - 10, 2012/03

The technical present status of hydrogen production process using IS thermochemical cycle was introduced. This process is experimentally investigated in Japan, U.S.A., Germany, France, Italy, India, China and Korea. Japan Atomic Energy Agency succeeded in consecutive hydrogen production as a proof examination. The trend of the research and development about the reactions, separation technology, device materials and the process equipment were reported. Thermochemical ammonia production cycle was also introduced. This new cycle is named ISN cycle which was modified from IS cycle in order to produce ammonia from water and nitrogen.

Journal Articles

Effects of chemical composition and dose on microstructure evolution and hardening of neutron-irradiated reactor pressure vessel steels

Takeuchi, Tomoaki; Kuramoto, Akira*; Kameda, Jun*; Toyama, Takeshi*; Nagai, Yasuyoshi*; Hasegawa, Masayuki*; Okubo, Tadakatsu*; Yoshiie, Toshimasa*; Nishiyama, Yutaka; Onizawa, Kunio

Journal of Nuclear Materials, 402(2-3), p.93 - 101, 2010/07

 Times Cited Count:58 Percentile:96.25(Materials Science, Multidisciplinary)

This study reports the effects of the composition and dose on microstructure evolution and hardening in high- and low-impurity A533B-1 steels neutron-irradiated in a wide range from 0.32 to 9.9 $$times$$ 10$$^{19}$$ n cm$$^{-2}$$ (E $$>$$ 1 MeV) under a constant high flux at JMTR. The early hardening was found to be caused by mainly matrix defects. The gradual hardening after middle stage of irradiation was found to be caused by the formation of Cu rich clusters (CRCs) and Mn-Ni-Si rich clusters (MNSCs), respectively, in the high- and low-impurity steels. By applying a RB model, it was found that the dislocation-pinning strength of the CRCs and MNSCs is almost the same. Moreover, the high-impurity steel subjected to the highest dose revealed the formation of MNSCs.

Journal Articles

Design of the shift bump magnets for the beam injection of the 3-GeV RCS in J-PARC

Takayanagi, Tomohiro; Kamiya, Junichiro; Watanabe, Masao; Ueno, Tomoaki*; Yamazaki, Yoshishige; Irie, Yoshiro; Kishiro, Junichi; Sakai, Izumi*; Kawakubo, Toshimichi*; Tounosu, Shigeki*; et al.

IEEE Transactions on Applied Superconductivity, 16(2), p.1366 - 1369, 2006/06

 Times Cited Count:8 Percentile:43.82(Engineering, Electrical & Electronic)

The injection system of the 3-GeV RCS in J-PARC is composed of four main orbit bump magnets (shift bump) to merge the injection beam with the circulating beam. The magnetic field design and the structural analysis of the shift bump magnets have been performed using 3D magnetic and mechanical codes. In this paper, the design of the bending magnets is reported.

Journal Articles

Development of superconducting proton linac for ADS

Ouchi, Nobuo; Akaoka, Nobuo*; Asano, Hiroyuki*; Chishiro, Etsuji; Namekawa, Yuya*; Suzuki, Hiroyuki*; Ueno, Tomoaki*; Noguchi, Shuichi*; Kako, Eiji*; Ouchi, Norihito*; et al.

Proceedings of 4th International Workshop on the Utilisation and Reliability of High Power Proton Accelerators, p.175 - 183, 2005/11

no abstracts in English

Journal Articles

Design of the pulse bending magnets for the injection system of the 3-GeV RCS in J-PARC

Takayanagi, Tomohiro; Irie, Yoshiro; Kamiya, Junichiro; Watanabe, Masao; Watanabe, Yasuhiro; Ueno, Tomoaki*; Noda, Fumiaki*; Saha, P. K.; Sakai, Izumi*; Kawakubo, Toshimichi*

Proceedings of 2005 Particle Accelerator Conference (PAC '05) (CD-ROM), p.1048 - 1050, 2005/00

The pulse bending magnets for the injection system of the 3-GeV RCS in J-PARC has been designed. The injection system consists of the pulsed bending magnets, which are four horizontal bending magnets (shift bump) and four horizontal painting magnets (h-paint bump) for the injection bump orbit, and two vertical painting magnets (v-paint magnet). The injection beam energy and the extraction beam power are 400 MeV and 1 MW at 25 Hz repetition rate, respectively. The acceptance to include the injection beam, the painting beam and the circulating beam at the shift bump points is a 388 mm wide and a 242 mm high. The shift bump has been designed using a 3D magnetic analysis code, which accomplished less than 0.4 % field deviation under 0.26 T excitation level.

JAEA Reports

Feasibility Study on Commercialization of Fast Breeder Reactor Cycle Systems Interim Report of Phase II; Technical Study Report for Reactor Plant Systems

Konomura, Mamoru; Ogawa, Takashi; Okano, Yasushi; Yamaguchi, Hiroyuki; Murakami, Tsutomu; Takaki, Naoyuki; Nishiguchi, Youhei; Sugino, Kazuteru; Naganuma, Masayuki; Hishida, Masahiko; et al.

JNC TN9400 2004-035, 2071 Pages, 2004/06

JNC-TN9400-2004-035.pdf:76.42MB

The attractive concepts for Sodium-, lead-bismuth-, helium- and water-cooled FBRs have been created through using typical plant features and employing advanced technologies. Efforts on evaluating technological prospects of feasibility have been paid for these concepts. Also, it was comfirmed if these concepts satisfy design requierments of capability and performance presumed in the feasibilty study on commertialization of Fast Breeder Reactor Systems. As results, it was concluded that the selection of sodium-cooled reactor was most rational for practical use of FBR technologies in 2015.

Journal Articles

A Large-volume high-pressure and high-temperature apparatus for in situ X-ray observation, "${it SPEED-Mk.II}$"

Katsura, Tomoo*; Funakoshi, Kenichi*; Kubo, Atsushi*; Nishiyama, Norimasa*; Tange, Yoshinori*; Sueda, Yuichiro*; Kubo, Tomoaki*; Utsumi, Wataru

Physics of the Earth and Planetary Interiors, 143-144, p.497 - 506, 2004/06

 Times Cited Count:106 Percentile:86.67(Geochemistry & Geophysics)

no abstracts in English

Journal Articles

Progress in physics and technology developments for the modification of JT-60

Tamai, Hiroshi; Matsukawa, Makoto; Kurita, Genichi; Hayashi, Nobuhiko; Urata, Kazuhiro*; Miura, Yushi; Kizu, Kaname; Tsuchiya, Katsuhiko; Morioka, Atsuhiko; Kudo, Yusuke; et al.

Plasma Science and Technology, 6(1), p.2141 - 2150, 2004/02

 Times Cited Count:2 Percentile:6.52(Physics, Fluids & Plasmas)

The dominant issue for the the modification program of JT-60 (JT-60SC) is to demonstrate the steady state reactor relevant plasma operation. Physics design on plasma parameters, operation scenarios, and the plasma control method are investigated for the achievement of high-$$beta$$. Engineering design and the R&D on the superconducting magnet coils, radiation shield, and vacuum vessel are performed. Recent progress in such physics and technology developments is presented.

Journal Articles

The New large-volume high P-T apparatus for in situ X-ray observation, ${it SPEED-Mk.II}$

Katsura, Tomoo*; Funakoshi, Kenichi*; Nishiyama, Norimasa*; Kubo, Atsushi*; Tange, Yoshinori*; Sueda, Yuichiro*; Kubo, Tomoaki*; Utsumi, Wataru

Hoshako, 16(6), p.352 - 357, 2003/11

no abstracts in English

Journal Articles

Objectives and design of the JT-60 superconducting tokamak

Ishida, Shinichi; Abe, Katsunori*; Ando, Akira*; Chujo, T.*; Fujii, Tsuneyuki; Fujita, Takaaki; Goto, Seiichi*; Hanada, Kazuaki*; Hatayama, Akiyoshi*; Hino, Tomoaki*; et al.

Nuclear Fusion, 43(7), p.606 - 613, 2003/07

no abstracts in English

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