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Kasahara, Naoto*; Yamano, Hidemasa; Nakamura, Izumi*; Demachi, Kazuyuki*; Sato, Takuya*; Ichimiya, Masakazu*
Transactions of the 27th International Conference on Structural Mechanics in Reactor Technology (SMiRT 27) (Internet), 8 Pages, 2024/03
In this study, we propose failure mitigation methods by application of passive safety structures. The idea of the passive safety structures was applied to next generation fast reactors under high temperature conditions and excessive earthquake conditions.
Dong, F.*; Chen, S.*; Demachi, Kazuyuki*; Yoshikawa, Masanori; Seki, Akiyuki; Takaya, Shigeru
Nuclear Engineering and Design, 404, p.112161_1 - 112161_15, 2023/04
Times Cited Count：14 Percentile：98.87(Nuclear Science & Technology)Kasahara, Naoto*; Yamano, Hidemasa; Nakamura, Izumi*; Demachi, Kazuyuki*; Sato, Takuya*; Ichimiya, Masakazu*
Transactions of the 26th International Conference on Structural Mechanics in Reactor Technology (SMiRT-26) (Internet), 8 Pages, 2022/07
Utilizing fracture control, we are developing a technology to suppress the expansion of damage caused by an event that exceeds the design assumption. We made a plan to develop three issues; (1) Technology for mitigating failure consequence at extremely high temperatures, (2) Technology for mitigating failure consequence against excessive earthquakes, and (3) Methodology for improving reactor structure resilience.
Tamai, Hiroshi; Demachi, Kazuyuki*
Genshiryoku Heiwa Riyo To Kakufukakusan, Kakusekyuritei; NSA/Commentaries, No.25, p.199 - 202, 2020/06
Education on nuclear non-proliferation and nuclear security in the University of Tokyo is provided at the Department of Nuclear Engineering and Management for master's course graduate students and at the Nuclear Professional School for career experts. In this paper, both the courses are introduced and their education contents on nuclear non-proliferation and nuclear security are briefly described.
Suzuki, Mitsutoshi; Demachi, Kazuyuki*
Journal of Nuclear Science and Technology, 55(5), p.559 - 567, 2018/05
Times Cited Count：3 Percentile：27.63(Nuclear Science & Technology)Facility design of nuclear power plant for a sabotage protection is investigated and an effect of the design change for damage control on reduction of sabotage risk is shown using the vital area identification methodology. The loss of offsite power leading to the station blackout is assumed to be a typical example for further evaluation. In this study, the vulnerability of target set is defined as the multiplication of the accessibility, the distribution of target and the degree of adversary's interference. The built-in measures for damage control are of vital importance in case of the existence of adversary's interference until neutralization. It is confirmed that not only the physical protection system but also the facility design play an important role in the effective and efficient sabotage protection. It is very important to introduce a security by design approach in an initial stage of the NPP construction while considering the interface between safety and security.
Goto, Minoru; Demachi, Kazuyuki*; Ueta, Shohei; Nakano, Masaaki*; Honda, Masaki*; Tachibana, Yukio; Inaba, Yoshitomo; Aihara, Jun; Fukaya, Yuji; Tsuji, Nobumasa*; et al.
Proceedings of 21st International Conference & Exhibition; Nuclear Fuel Cycle for a Low-Carbon Future (GLOBAL 2015) (USB Flash Drive), p.507 - 513, 2015/09
A concept of a plutonium burner HTGR named as Clean Burn, which has a high nuclear proliferation resistance, had been proposed by Japan Atomic Energy Agency. In addition to the high nuclear proliferation resistance, in order to enhance the safety, we propose to introduce PuO
-YSZ TRISO fuel with ZrC coating to the Clean Burn. In this study, we conduct fabrication tests aiming to establish the basic technologies for fabrication of PuO-YSZ TRISO fuel with ZrC coating. Additionally, we conduct a quantitative evaluation of the security for the safety, a design of the fuel and the reactor core, and a safety evaluation for the Clean Burn to confirm the feasibility. This study is conducted by The University of Tokyo, Japan Atomic Energy Agency, Fuji Electric Co., Ltd., and Nuclear Fuel Industries, Ltd. It was started in FY2014 and will be completed in FY2017, and the first year of the implementation was on schedule.
Ohgama, Kazuya; Ando, Yoko; Yamaguchi, Mika; Ikuta, Yuko; Shinohara, Nobuo; Murakami, Hiroyuki; Yamashita, Kiyonobu; Uesaka, Mitsuru*; Demachi, Kazuyuki*; Komiyama, Ryoichi*; et al.
JAEA-Review 2013-004, 76 Pages, 2013/05
JAEA-Review-2013-004.pdf:13.53MB
JAEA together with the Japan Nuclear Human Resource Development Network (JN-HRD Net), the University of Tokyo (UT) and the Japan Atomic Industrial Forum (JAIF) cohosted the IAEA-Nuclear Energy Management School in Tokai Village, aiming that Japan will be the center of nuclear HRD in the Asian region. In the school, not only lectures by IAEA experts, but also lectures by Japanese experts and technical visits were included for foreign participants. The school contributed to the internationalization of Japanese young professionals, development of nuclear human resource of other countries, and enhancement of cooperation between IAEA and Japan. Additionally, collaborative relationship within JN-HRD Net was strengthened by the school. In this report, findings obtained during the preparatory work and the school period are reported for future international nuclear HRD activities in Japan.
Miya, Kenzo; Demachi, Kazuyuki*; Aoto, Kazumi;
JNC TN9400 2002-021, 22 Pages, 2002/04
JNC-TN9400-2002-021.pdf:1.08MB
Establishment of evaluation methods of material degradation before crack initiation is needed very much to enhance the reliability of structural components. We remark magnetic methods in this report. Our objectives are to reveal the relation between degradation and magnetic property and to develop evaluation methods of material degradation, especially plastic deformation and stress corrosion cracking (SCC). In the former part of this report, evaluation methods for plastic deformation are discussed. At first, the study that shows the relation between the magnetic flux leakage and plastic deformation is reviewed. We developed the inverse analysis method of magnetization to specify the degradation distribution. Moreover, we propose inverse analysis of magnetic susceptibility for quantitative evaluation. In the latter part, the topic is SCC. We measured the magnetic flux leakage from the sample induced a SCC crack (Inconel-600). Inconel-600 is a paramagnetic material at room temperature but the sample shows ferromagnetic and the magnetic flux leakage was changed near the SCC crack. The possibility of detection of a SCC crack is shown by the inverse analysis result from the magnetic flux leakage. Finany, it is recognized by observation of the micro magnetic distributions by using a magnetic force microscope that the magnetization has relation with chromium depletion near grain boundaries and it is weak near the SCC crack. From these results, the magnetic method is very effective for evaluation of degradation.
Demachi, Kazuyuki*; Miya, Kenzo
JNC TN9400 2001-066, 21 Pages, 2001/03
JNC-TN9400-2001-066.pdf:0.55MB
The quantitative evaluation of cracks in structural components is necessary to maintain its safety and to estimate its life. Moreover, the establishment of diagnosis technique of the material degradation before the appearance of crack is necessary for the higher safety. In this research, the magnetic value is chosen as the parameter for the material degradation. The crack is considered to occur by the local stress concentration, and the magnetic value is one of the most sensitive parameter for the elastic deformation of the material. The research about leak field change of SUS stainless steel due to the stress was performed by Chen et al,. The measured leak magnetic flux density is large around a crack. From such a measurement result, it is found that the leak is related with the elastic deformation of the material. The numerical method based on the Neural Network was developed for the inverse analysis of the magnetization in the specimen from the measured leak field. It is found the magnetization is large near the edges of the crack. The magnetic flux density obtained from this simulation result of the magnetization corresponds to the leak field. Then the inverse analysis method was developed to estimate the distribution of susceptibility in the specimen from the measured leak fie1d. Its results are denoted in the full report. The new nondestructive evaluation method was supposed for the diagnosis of the degradation of the material before the appearance of cracks.
Kasahara, Naoto*; Yamano, Hidemasa; Nakamura, Izumi*; Demachi, Kazuyuki*; Sato, Takuya*; Ichimiya, Masakazu*
no journal, ,
Utilizing fracture control, we are developing a technology to suppress the expansion of damage caused by an event that exceeds the design assumption. We proceeded with the study of concrete measures by taking the reactor vessel and piping of the next-generation fast reactor at ultra-high temperatures and during an excessive earthquake as an example.
Demachi, Kazuyuki*; Dong, F.*; Abe, Toru*; Chen, S.*; Takaya, Shigeru; Seki, Akiyuki; Yoshikawa, Masanori; Miki, Daisuke*
no journal, ,
Kasahara, Naoto*; Yamano, Hidemasa; Nakamura, Izumi*; Demachi, Kazuyuki*; Sato, Takuya*; Ichimiya, Masakazu*
no journal, ,
This report proposes passive safety structures which avoid catastrophic failure leading to the loss of safety function by naturally mitigating loads as a result of early occurrence of small failure mode on the safety function as new countermeasures in structural areas beyond design basis events.
Demachi, Kazuyuki*; Kuwabara, Yuto*; Chen, S.*; Kasahara, Naoto*; Nishino, Hiroyuki; Onoda, Yuichi; Kurisaka, Kenichi
no journal, ,
no abstracts in English
Onoda, Yuichi; Nishino, Hiroyuki; Kurisaka, Kenichi; Yamano, Hidemasa; Demachi, Kazuyuki*
no journal, ,
In order to evaluate the effectiveness of the measures for improving resilience at ultra-high temperatures, a concept of evaluation focusing on core damage frequency was proposed. Assuming loss of heat removal systems event after reactor shutdown which may result in core damage in sodium-cooled fast reactors, the measures for improving resilience which enable to recover the safety functions at ultra-high temperatures are identified: one is to retain the primary coolant using failure mitigation technology, and the other is to add a heat removal system that can be used under ultra-high temperature conditions. The core damage frequencies were calculated preliminarily and their reduction effect was estimated by comparing them before and after the introduction of the measures for improving resilience.
Kasahara, Naoto*; Demachi, Kazuyuki*; Sato, Takuya*; Ichimiya, Masakazu*; Wakai, Takashi; Yamano, Hidemasa; Nakamura, Izumi*
no journal, ,
The conventional purpose in the field of structural strength has been to prevent damage to design basis events (DBE). For beyond design basis events (BDBE), it is necessary to mitigate the impact on safety on the premise that damage will occur. The authors propose a mitigation method that suppresses the consequence into a fracture mode with a large impact by reducing the load due to a fracture with a small impact on safety. We will introduce the research results for individual component, extend the applicable area to systems of components, and propose a new approach that contributes to improving plant safety.
Kasahara, Naoto*; Yamano, Hidemasa; Nakamura, Izumi*; Demachi, Kazuyuki*; Sato, Takuya*; Ichimiya, Masakazu*
no journal, ,
This paper reports a technology to suppress the expansion of damage caused by beyond design basis events (very high temperature in a severe accident or excessive earthquake), and the outline of the development plan for improving the resilience of the reactor structure (resistance and resilience to deterioration of safety performance).
Demachi, Kazuyuki*; Chen, S.*; Dong, F.*; Yoshikawa, Masanori; Seki, Akiyuki; Takaya, Shigeru
no journal, ,
no abstracts in English
Kuwahara, Yuto*; Demachi, Kazuyuki*; Chen, S.*; Kasahara, Naoto*; Nishino, Hiroyuki; Onoda, Yuichi; Kurisaka, Kenichi
no journal, ,
no abstracts in English
Nishino, Hiroyuki; Onoda, Yuichi; Kurisaka, Kenichi; Yamano, Hidemasa; Demachi, Kazuyuki*
no journal, ,
In order to evaluate the effectiveness of the measures for improving resilience against excessive earthquake, this study assumed to improve seismic safety margin of components of heat removal system as the measures against loss of heat removal systems event after reactor shutdown. The core damage frequency was calculated and the reduction effect of it was estimated by comparing it before and after the introduction of the measures for improving resilience.
Dong, F.*; Chen, S.*; Demachi, Kazuyuki*; Yoshikawa, Masanori; Seki, Akiyuki; Takaya, Shigeru
no journal, ,
