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Arai, Yoichi; Watanabe, So; Hasegawa, Kenta; Okamura, Nobuo; Watanabe, Masayuki; Takeda, Keisuke*; Fukumoto, Hiroki*; Ago, Tomohiro*; Hagura, Naoto*; Tsukahara, Takehiko*
Nuclear Instruments and Methods in Physics Research B, 542, p.206 - 213, 2023/09
Suzuki, Seiya; Arai, Yoichi; Okamura, Nobuo; Watanabe, Masayuki
Journal of Nuclear Science and Technology, 60(7), p.839 - 848, 2023/07
Times Cited Count:0 Percentile:0.01(Nuclear Science & Technology)The fuel debris, consisting of nuclear fuel materials and reactor structural materials, generated in the accident of Fukushima Daiichi Nuclear Power Plant can become deteriorated like rocks under the changes of environmental temperature. Although the fuel debris have been cooled by water for 10 years, they are affected by seasonal and/or day-and-night temperature changes. Therefore, in evaluating the aging behavior of the fuel debris, it is essential to consider the changes in environmental temperature. Assuming that the fuel debris are deteriorated, radioactive substances that have recently undergone micronization could be eluted into the cooling water, and such condition may affect defueling methods. We focused on the effect of repeated changes in environmental temperature on the occurrence of cracks, and an accelerated test using simulated fuel debris was carried out. The length of the crack increases with increasing number of heat cycle; therefore, the fuel debris become brittle by stress caused by thermal expansion and contraction. In conclusion, it was confirmed that the mechanical deterioration of the fuel debris is similar to that of rocks or minerals, and it became possible to predict changes in the length of the crack in the simulated fuel debris and environmental model.
Miyazaki, Yasunori; Sano, Yuichi; Okamura, Nobuo; Watanabe, Masayuki; Koka, Masashi*
QST-M-29; QST Takasaki Annual Report 2019, P. 72, 2021/03
no abstracts in English
Nakayoshi, Akira; Suzuki, Seiya; Okamura, Nobuo; Watanabe, Masayuki; Koizumi, Kenji
Journal of Nuclear Science and Technology, 55(10), p.1119 - 1129, 2018/10
Times Cited Count:2 Percentile:21.23(Nuclear Science & Technology)Kitagaki, Toru; Hoshino, Takanori; Yano, Kimihiko; Okamura, Nobuo; Ohara, Hiroshi*; Fukasawa, Tetsuo*; Koizumi, Kenji
Journal of Nuclear Engineering and Radiation Science, 4(3), p.031011_1 - 031011_7, 2018/07
Hoshino, Takanori; Kitagaki, Toru; Yano, Kimihiko; Okamura, Nobuo; Ohara, Hiroshi*; Fukasawa, Tetsuo*; Koizumi, Kenji
Proceedings of 23rd International Conference on Nuclear Engineering (ICONE-23) (DVD-ROM), 6 Pages, 2015/05
Sakamoto, Atsushi; Sano, Yuichi; Takeuchi, Masayuki; Okamura, Nobuo; Koizumi, Kenji
Proceedings of 23rd International Conference on Nuclear Engineering (ICONE-23) (DVD-ROM), 5 Pages, 2015/05
Kofuji, Hirohide; Okamura, Nobuo; Mizuguchi, Koji*; Myochin, Munetaka
Journal of Nuclear Science and Technology, 45(9), p.942 - 950, 2008/09
Times Cited Count:1 Percentile:17.03(Nuclear Science & Technology)In the oxide electrowinning method of nuclear fuel recycling, the applicability of the pulse electrolysis method to the MOX co-deposition process was evaluated. Several experiments were conducted involving uranium, plutonium, and elements simulating fission product (FP) or corrosion product (CP). Through study of the results of these experiments, the influences of the impurities and the effect of the waveform of electrolysis pulses on the electro-deposit were clarified. As a result, pulse electrolysis conditions which could restrain Pu enrichment of the deposited MOX were confirmed. Furthermore, it was found that the element distribution in the MOX granule obtained by the pulse electrolysis was homogenized, which is well suited for nuclear fuel fabrication. Finally, a qualitative model of the pulse electrolysis reaction near the field of cathode surface is proposed.
Okamura, Nobuo; Takeuchi, Masayuki; Ogino, Hideki; Kase, Takeshi; Koizumi, Tsutomu
Proceedings of International Conference on Advanced Nuclear Fuel Cycles and Systems (Global 2007) (CD-ROM), p.1070 - 1075, 2007/09
no abstracts in English
Okamura, Nobuo; Koizumi, Kenji; Washiya, Tadahiro; Aose, Shinichi
Proceedings of 13th International Conference on Nuclear Engineering (ICONE-13) (CD-ROM), 0 Pages, 2005/05
In Japan Nuclear Cycle Development Institute (JNC), a commercial scale electrolyzer, whose capacity is 25tHM/y, is been developing to be used in an oxide electrowinning process, a kind of non-aqueous reprocessing process. It has some significant subjects that must be solved before introduced in a commercial reprocessing plant. It developed in JNC has some innovative characteristics, such as cold crucible induction melting (CCIM), to cope with those subjects. But these characteristics make it difficult to arrange the internal components because of a narrow and deep shape of a crucible. So two kinds of analysis systems with computer were constructed to help a design of the internal constitution. One of them is to evaluate the temperature distribution in the crucible and another is to evaluate the shape of deposits. In this study, the internal constitution in the commercial scale electrolyzer was designed by using them finally.
Okamura, Nobuo; Tozawa, Katsuhiro; Sato, Koji
Proceedings of 11th International Conference on Nuclear Engineering (ICONE-11) (CD-ROM), 0 Pages, 2003/00
None
; Tozawa, Katsuhiro;
JNC TN9400 2002-041, 57 Pages, 2002/07
The operation of the plant with the non-aqueous reprocessing technology depends on the materials handling equipment closely. Because the value of decontamination factor of the products in the plant is low, treatment of nuclear materials requires remote operation technology. So the system for the evaluation of materials flow in the plant was built to evaluate the production ability of the plant and to check out the plant operation from the viewpoint of materials flow. The system is only based on information of the treatment abilities of materials handling machines and process installations and the arrangement of process installations in the reprocessing cell that influences a way to operate materials handling machines intensely. Therefore the system can be used to estimate the characteristics of non-aqueous plants that are not in detail design stage. The amount of production and the characteristics of the oxide electrowinning plant (operation term 200days/year, plant capacity 50tHM/year in design) designed in Feasibility Study Phase-1 were estimated using the system. The results show that the practical amount of production of the plant design is about 88% of the designed value. To increase the amount of production, it is more useful to speed up materials handling machine time than to install new installations or to give priority to conduct bottleneck processes. It is because materials handling influences the production ability of the plant deeply.
Fujioka, Tsunaaki; ; ; ; ; *; *
JNC TY9400 2001-028, 129 Pages, 2001/12
no abstracts in English
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JNC TN9400 2001-060, 73 Pages, 2001/04
The electrorefining using molten salt is employed in some pyrochemical reprocessing systems. The material behavior in this process, however, is not sufficiently clarified because of the lack of experimental data. The objective of this study is to develop the analysis code of the material behavior. There are two kinds of codes for the analysis of electrorefining process. One is based on the model of material behavior in macroscopic region, which calculates the electrical potential distribution and the current density distribution from electrical potential difference between anodes and cathodes, and obtain the amount of deposited material with spatial distribution on cathode surface. The other is based on the model of material behaviors in microscopic region, which calculates material concentrations on cathode surface with the Nernst's equation from cathode electrical potential, and estimates deposition yields to solve the diffusion equation with material concentrations in molten salt and on cathode surface. In this study, the analysis code, that is able to treat material behaviors with the model of ones in macroscopic and microscopic region and consider molten salt flow, has been developed. As a result, it is confirmed that the segregation of the deposit on cathod caused by the current density distribution is disappeared by stirring molten salt and PuO is efficiently recovered in the MOX electrolysis in which Pu4 is oxidized to PuO by O and PuO is reduced by electrochemical reaction.
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JNC TN9400 2001-059, 51 Pages, 2001/04
Pyrochemical reprocessing is thought to be promising process for FBR fuel cycle mainly from the economical viewpoint. However, the material behavior in the process is not clarified enough because of the lack of experimental data. The authors have been developed the object-oriented analysis code for the estimation of material balance in the process, which has the flexible applicability for the change of process flow sheet. The objective of this study is to modify the code so as to analyze the holdup of nuclear materials in the pyrochemical process from the viewpoint of safeguard, because of the possibility of larger amount of the holdup in the process compared with aqueous process. As a result of the modification, the relationship between the production of nuclear materials and its holdup in the process can be evaluated by the code.
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JNC TN9400 2000-034, 48 Pages, 2000/03
The study and the development to put FBR (Fast Breeder Reactor) to practical use have been doing. So many kinds of technologies are investigated to construct nuclear fuel recycle received to the society. The most important aim of reprocessing has been to extract U and Pu from spent fuels effectively, but, now, the demands for reprocessing are many kinds on nuclear fuel recycle system's construction. These need to be accepted sufficiently. The system that consists of electrolysis, extraction, with molten salt and melting metal, volatilization and condensation using the difference of vapor pressure is suggested, because, differently from LWR (Light Water Reactor), FBR can use the low decontamination factor's fuel. When the engineering scale plant is designed, the dry reprocessing has unsolved problems(ex. process flow) because of less demonstrative scale plants of the dry reprocessing than ones of the wet reprocessing. So the analysis and the estimation of mass balance that is most fundamental in the dry reprocessing system's design need to keep up with the system's alteration (to add new processes etc.) flexibly. This study aim is to develop the mass balance estimation code of dry reprocessing that satisfies the demand mentioned above.
Okamura, Nobuo; Koizumi, Tsutomu; Fukushima, Mineo; Kurata, Masaki; Sakamura, Yoshiharu*
no journal, ,
no abstracts in English
Okamura, Nobuo; Ogino, Hideki; Arai, Yoichi; Kase, Takeshi; Koizumi, Tsutomu; Idesaki, Akira; Morishita, Norio; Oshima, Takeshi; Kojima, Takuji
no journal, ,
no abstracts in English