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Machida, Masahiko; Yamada, Susumu; Kim, M.; Okumura, Masahiko; Miyamura, Hiroko; Shikaze, Yoshiaki; Sato, Tomoki*; Numata, Yoshiaki*; Tobita, Yasuhiro*; Yamaguchi, Takashi; et al.
RIST News, (69), p.2 - 18, 2023/09
The contamination of radioactive materials leaked from the reactor has resulted in numerous hot spots in the Fukushima Daiichi Nuclear Power Station (1F) building, posing obstacles to its decommissioning. In order to solve this problem, JAEA has conducted research and development of the digital technique for inverse estimation of radiation source distribution and countermeasures against the estimated source in virtual space for two years from 2021 based on the subsidy program "Project of Decommissioning and Contaminated Water Management" performed by the funds from the Ministry of Economy, Trade and Industry. In this article, we introduce the results of the project and the plan of the renewal project started in April 2023. For the former project, we report the derivative method for LASSO method considering the complex structure inside the building and the character of the source and show the result of the inverse estimation using the method in the real reactor building. Moreover, we explain the platform software "3D-ADRES-Indoor" which integrates these achievements. Finally, we introduce the plan of the latter project.
Machida, Masahiko; Yamada, Susumu; Kim, M.; Okumura, Masahiko; Miyamura, Hiroko; Malins, A.; Shikaze, Yoshiaki; Sato, Tomoki*; Numata, Yoshiaki*; Tobita, Yasuhiro*; et al.
RIST News, (68), p.3 - 19, 2022/09
no abstracts in English
Oka, Hiroshi; Tanno, Takashi; Yano, Yasuhide; Otsuka, Satoshi; Kaito, Takeji; Tachi, Yoshiaki
Journal of Nuclear Materials, 547, p.152833_1 - 152833_7, 2021/04
Times Cited Count：10 Percentile：73.48(Materials Science, Multidisciplinary)In order to evaluate the stability of nano-sized oxide particles and matrix structure of ODS cladding tube, which are the determinants of their high temperature strength, the microstructural observation was carried out after internal pressurized creep test at 700
C for over 45,000 hours. The specimens were the as-received and crept specimens of 9Cr-ODS steel with tempered martensite and 12Cr-ODS steel with recrystallized ferrite. Small platelet was cut out from the crept pressurized tube, then thinned to foil. Microstructural observation was conducted with TEM JEOL 2010F. As a result of the observation, it was confirmed that the size and number density of the nano-sized particles were almost unchanged even after the creep test. In addition, the tempered martensite structure, which is one of the determinants of the creep strength of 9Cr-ODS steel, was not significantly different between the as-received and crept specimen, indicating the stability of their matrix structure.
Otsuka, Satoshi; Tanno, Takashi; Oka, Hiroshi; Yano, Yasuhide; Tachi, Yoshiaki; Kaito, Takeji; Hashidate, Ryuta; Kato, Shoichi; Furukawa, Tomohiro; Ito, Chikara; et al.
2018 GIF Symposium Proceedings (Internet), p.305 - 314, 2020/05
Oxide Dispersion Strengthened (ODS) steel has been developed worldwide as a high-strength and radiation-tolerant steel used for advanced nuclear system. Japan Atomic Energy Agency (JAEA) has been developing ODS steel as the primary candidate material of Sodium cooled Fast Reactor (SFR) high burn-up fuel cladding tube. Application of high burn-up fuel to SFR core can contribute to improvement of economical performance of SFR in conjunction with volume and hazardousness reduction of radioactive waste. This paper described the current status and future prospects of ODS tempered martensitic steel development in JAEA for SFR fuel application.
Chiba, Satoshi*; Wakabayashi, Toshio*; Tachi, Yoshiaki; Takaki, Naoyuki*; Terashima, Atsunori*; Okumura, Shin*; Yoshida, Tadashi*
Scientific Reports (Internet), 7(1), p.13961_1 - 13961_10, 2017/10
Times Cited Count：47 Percentile：97.62(Multidisciplinary Sciences)Transmutation of long-lived fission products (LLFPs: 
Se, 
Zr, 
Tc, 
Pd, 
I, and 
Cs) into short-lived or non-radioactive nuclides by fast neutron spectrum reactors without isotope separation has been proposed as a solution to the problem of radioactive wastes disposal. Despite investigation of many methods, such transmutation remains technologically difficult. To establish an effective and efficient transmutation system, we propose a novel neutron moderator material, yttrium deuteride (YD
), to soften the neutron spectrum leaking from the reactor core. Neutron energy spectra and effective half-lives of LLFPs, transmutation rates, and support ratios were evaluated with the continuous-energy Monte Carlo code MVP-II/MVP-BURN and the JENDL-4.0 cross section library. With the YD moderator in the radial blanket and shield regions, effective half-lives drastically decreased from 10
to 10
years and the support ratios reached 1.0 for all six LLFPs. This successful development and implementation of a transmutation system for LLFPs without isotope separation contribute to developing a self-consuming cycle of LLFPs using fast spectrum reactors to reduce radioactive waste.
Ozu, Akira; Tachi, Yoshiaki; Arita, Yuji*
Reza Kenkyu, 42(12), p.913 - 917, 2014/12
Laser-induced breakdown spectroscopy (LIBS) analysis has been applied to the molten alloy production process, in which simulated metals (Zr, Cu, Sm, Ce) are used instead of nuclear metallic fuels contained minor actinide (MA), with the aim of in-situ monitoring the elementary composition of the surface of the molten alloy in a chamber and vapor particles generated from the surface of the molten alloy. The variation in the ratio of elementary composition of the surface of the molten alloy in the crucible was successfully observed depending on temperature of the crucible. The elementary composition of the vapor particles appeared in the molten alloy chamber was also measured. The practical experimental results show that LIBS technique is very useful for investigating the elementary composition in the process and understanding the behavior of molten alloy in the crucible.
Ishimi, Akihiro; Tachi, Yoshiaki; Katsuyama, Kozo; Misawa, Susumu*
JAEA-Data/Code 2014-012, 72 Pages, 2014/08
JAEA-Data-Code-2014-012.pdf:82.93MB
The Fuels Monitoring Section (FMS) of Japan Atomic Energy Agency (JAEA) has carried out examination of the fuel assemblies irradiated at Experimental Fast Reactor Joyo to verify about deformation and damage using X-ray computed tomography (CT) technique. This technique can observe deformation and internal information of the irradiated fuel assembly without dismantling and thus can apply to inspections of the irradiated fuel assembly in Fukushima Daiichi Nuclear Power Plant (1F). In order to obtain X-ray CT basic data for 1F fuel assembly inspection, the simulated specimens were made and the X-ray CT examinations were performed in the Fuels Monitoring Facility (FMF). This paper compiled the data about the X-ray CT examination of the simulated specimens.
Donomae, Takako; Katsuyama, Kozo; Tachi, Yoshiaki; Maeda, Koji; Yamamoto, Masaya; Soga, Tomonori
Journal of Nuclear Science and Technology, 48(4), p.580 - 584, 2011/04
One of the challenges in developing a long-life control rod is to restrain absorber-cladding mechanical interaction (ACMI). Its lifetime was limited by ACMI, which is induced by the swelling and relocation of B
C pellets. To restrain ACMI, a shroud tube was inserted into the gap between the BC pellets and the cladding tube. And sodium was selected as bonding material instead of helium to restrain increases in the pellet temperature. As a result of these improvements, the estimated lifetime of the control rod at Joyo was doubled. In this paper, the results of post irradiation examination are reported.
Tachi, Yoshiaki; Wakabayashi, Toshio*
Transactions of the American Nuclear Society, 103(1), p.268 - 269, 2010/11
It is very attractive technique to transmute long-lived fission products such as iodine-129 included in spent fuel by using Fast Reactors (FRs) to minimize environmental burden and toxic risk due to high level waste disposal. Iodine has low melting point (386K) and low boiling points (457K) compared with FR core temperature. Furthermore, it is corrosive against iron based materials. Then, it is the most important issue to search suitable chemical forms for FR core conditions, having high stability at elevated temperature and good compatibility with cladding material. From the viewpoint of melting point, nuclides generation by neutron irradiation, reactivity with stainless steel, easy fabrication method and recyclability, 5 kinds of iodides of CuI, MgI, YI
, RbI and YI were selected as the candidate chemical form of iodine for transmutation in FR. In order to evaluate stability of the candidate iodides at elevated temperature, TG-DTA of CuI, RbI, BaI and YI were performed. According to TG-DTA results, no significant mass change showed in BaI beyond those temperatures. Mass of CuI, RbI and YI started to be lost severely at the lower temperature than their melting points. Compatibility test between iodides and cladding materials were conducted. Cladding materials in contact with iodides were heated in a capsule filled with pure Ar gas at 873K for 5000h maximum. Results of cross-section observation showed that MgI and YI made pit corrosion on SUS316 and ODS. It appeared that the upper part of the inner surface test capsules with RbI, YI were degraded severely. Based on the experimental results, the most applicable iodide for transmutation by FR is BaI from the viewpoints of stability at elevated temperature and compatibility with cladding material.
Yamashita, Shinichiro; Yano, Yasuhide; Tachi, Yoshiaki; Akasaka, Naoaki
Journal of Nuclear Materials, 386-388, p.135 - 139, 2009/04
Times Cited Count：14 Percentile：65.70(Materials Science, Multidisciplinary)The heat resistant 11Cr ferritic/martensitic steels were irradiated at 400-670 C up to 100 dpa in FFTF and JOYO. The microstructures of unirradiated 11Cr ferritic/martensitic steels consist of laths, dislocation, and carbide. Almost of the prior austenitic boundaries (PABs) were partially decorated with carbides. It was observed from the results of post irradiation microstructural examinations that the irradiation-induced microstructures were classified into the following three types depending on irradiation temperature; (1) When irradiated at 400-450 C, both dislocation loops and cavities with less than 30 nm in diameter were formed in the ferrite phase. On the other hand, the void swelling was about 0.05%. (2) In the case of irradiation at moderate temperature (500-600 C), the precipitates formation M
C
carbide was primarily dominated. It was a most noticeable microstructural feature that the carbides; MC and MC grew and covered the PABs at this temperature range. (3) Finally, when irradiation temperature was above 650 C microstructures were drastically-changed. Microstructural observations revealed that formation and growth of equi-axial grain occurred in addition to recovery of laths, growth of carbides simultaneously at high temperature. This remarkable microstructural change might be closely related to a severe degradation in the mechanical properties.
BCMorohashi, Yuko; Maruyama, Tadashi*; Donomae, Takako; Tachi, Yoshiaki; Onose, Shoji
Journal of Nuclear Science and Technology, 45(9), p.867 - 872, 2008/09
Times Cited Count：13 Percentile：60.45(Nuclear Science & Technology)BC and recovery by annealingDonomae, Takako; Tachi, Yoshiaki; Sekine, Manabu*; Morohashi, Yuko; Akasaka, Naoaki; Onose, Shoji
Journal of the Ceramic Society of Japan, 115(1345), p.551 - 555, 2007/09
Times Cited Count：4 Percentile：28.30(Materials Science, Ceramics)Use of moderator materials in Fast Breeder Reactor (FBR) is effective for transmutation technology, and BC is one of the candidates. Up to now, the behavior of 
BC as the Control rod material is well known, but that of BC is hardly investigated. In this paper, the radiation effects of BC pellets, neutron irradiated in the experimental fast reactor JOYO were studied. From the experimental results, it was observed that no macro-cracks were recognized in the irradiated BC pellets. But, bubble nucleation was found in grain and along grain boundaries of BC. And, it was shown that the conductivity of BC was higher than that of BC. During the annealing from room temperature to 1400C, three recovery stages were found on thermal conductivity. It was suggested that, the recovery of BC was related to the dispersion behavior of helium. Judging from these results, as BC was mechanically more stable compared with BC under irradiation, it was shown that BC had high applicability for a moderator.
Osaka, Masahiko; Serizawa, Hiroyuki; Kato, Masato; Nakajima, Kunihisa; Tachi, Yoshiaki; Kitamura, Ryoichi; Miwa, Shuhei; Iwai, Takashi; Tanaka, Kenya; Inoue, Masaki; et al.
Journal of Nuclear Science and Technology, 44(3), p.309 - 316, 2007/03
Times Cited Count：31 Percentile：87.17(Nuclear Science & Technology)no abstracts in English
Donomae, Takako; Tachi, Yoshiaki; Matsumoto, Shinichiro
JAEA-Research 2006-033, 35 Pages, 2006/07
JAEA-Research-2006-033.pdf:8.59MB
no abstracts in English
Miwa, Shuhei; Osaka, Masahiko; Tachi, Yoshiaki; Tanaka, Kenya
JAEA-Research 2005-003, 25 Pages, 2006/01
JAEA-Research-2005-003.pdf:3.29MB
In the technology for transmutation of Minor Actinides (MAs) to stable and short-lived nuclides by irradiation in the reactor, one promising candidate for the MA-containing ceramic form is a composite of MA compound and inert matrix, so called "target". In this study, surrogate target which is the combination of CeO as a substitution of (Pu, Am)O with MgO as the inert matrix is fabricated by a simple process based on commercial manufacturing technology for the present fuel. Structural analyses are performed by XRD, SEM observation and EDS analysis. From the results of analysis, the targets with high density, high homogenous dispersion of sphere, non reaction phase are obtained. Thermal stability and thermal conductivity of fabricated target are investigated. Dissolubility to nitride solution, thermal stability and thermal conductivity of fabricated target are investigated.
-MgO composite as surrogate for actinide-containing target for use in nuclear fuelOsaka, Masahiko; Miwa, Shuhei; Tachi, Yoshiaki
Ceramics International, 32(6), p.659 - 663, 2006/00
Times Cited Count：22 Percentile：79.52(Materials Science, Ceramics)A simple fabrication process for the fabrication of CeO-MgO composite as surrogate for actinide-containing target for the use in nuclear field is established. The process is adaptable to the present manufacturing technology for the nuclear fuel. The manufactured target have good characteristics, e.g. high density, good appearance etc. In particular, although the shape of CeO2 is not ideal sphere as expected but elliptic, thermal conductivity measurement results show that the elliptic shape is not disadvantageous. It means that the present simple process is comparable to that of rather complicated one, advanced sol-gel supported process.
Osaka, Masahiko; Serizawa, Hiroyuki*; Kato, Masato; Inoue, Masaki; Nakajima, Kunihisa*; Tachi, Yoshiaki; Kitamura, Ryoichi; Oki, Shigeo; Miwa, Shuhei; Iwai, Takashi*; et al.
Proceedings of International Conference on Nuclear Energy System for Future Generation and Global Sustainability (GLOBAL 2005) (CD-ROM), 6 Pages, 2005/10
Development of minor actinide containing fuel/target, i.e., (Pu,Am)O-MgO, (Pu,Np)O-MgO, (U,Pu,Np)O, (U,Pu,Np)N and (Pu,Np,Zr)N, for the use in a future integrated system of fast reactor and accelerator driven system is underway as a collaborative work between JAERI and JNC. The present statuses of fabrication test and property measurements are given. Irradiation test in the experimental fast reactor JOYO is also mentioned.
Yamashita, Kiyonobu; Ozawa, Masaki; Ikegami, Tetsuo; Harada, Hideo; Osaka, Masahiko; Oki, Shigeo; Tachi, Yoshiaki; Furutaka, Kazuyoshi; Nakamura, Shoji
JNC TN9420 2004-001, 106 Pages, 2005/03
JNC-TN9420-2004-001.pdf:12.85MB
Research Evaluation Committee carried out a pre-evaluation of Research and Development of Partitioning and Transmutation Technology of Long-Lived-Nuclides namely, partitioning, nuclear data, reactor physics, fuel, creative transmutation technology, in Aug. 2000. Following results are obtained from the research and development. For example, two extract ant systems, capable of recovering all actinides in spent fuel, were newly nominated in partitioning technology. Also, neutron capture cross sections of 7 nuclides of MA and Fission Products (FP) were determined in nuclear data measurements. Some of those measurements are for the first time in the world. An advanced measurement system of a full solid angle Bi4Ge3O12 detector etc. was developed to measure the energy dependence of the neutron capture cross sections. These achievements in the first phase are summarized in the report to promote the research and development in the second phase effectively.
Akiyoshi, Masafumi; Akasaka, Naoaki; Tachi, Yoshiaki; Yano, Toyohiko*
Abstract p303,22-P-02, 303 Pages, 2003/00
Focusing on the cover layer materials (as the Radon Barrier Materials), which could have the effect to restrain the radon from scattering into the air and the effect of the radiation shielding, we produced the radon barrier materials with crude bentonite on an experimental basis, using the rotary type comprehensive unit for grinding and mixing, through which we carried out the evaluation of the characteristics thereof.
; Tachi, Yoshiaki; ; ; ; ;
JNC TY9400 2001-003, 111 Pages, 2000/11
JNC-TY9400-2001-003.pdf:5.11MB
no abstracts in English
