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Ota, Masakazu; Takahara, Shogo; Yoshimura, Kazuya; Nagakubo, Azusa; Hirouchi, Jun; Hayashi, Naho; Abe, Tomohisa; Funaki, Hironori; Nagai, Haruyasu
Journal of Environmental Radioactivity, 264, p.107198_1 - 107198_15, 2023/08
Times Cited Count:0 Percentile:0(Environmental Sciences)One of the current major radiation exposure pathways from the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident-fallout is inhalation of the re-suspended Cs occurring in air. While wind-induced soil particle resuspension has been recognized as a primary mechanism of Cs resuspension, studies following the FDNPP accident suggested that fungal spores can be a significant source of the atmospheric Cs particularly in the rural areas such as difficult-to-return zone (DRZ). To elucidate the relative importance of the two resuspension phenomena, we propose a model simulating resuspension of Cs as soil particles and fungal spores, and applied it to DRZ. Our model's calculation showed that soil particle resuspension was responsible for the surface-air Cs observed during winter-spring, but could not account for the higher Cs concentrations observed in summer-autumn. The higher concentrations in the summer-autumn were in general reproduced by implementing fungal spore Cs emission, that replenished low soil particle Cs resuspension in that period. According to our model's concept, Cs accumulation in fungal spores and high spore emission rate characterized by the rural environment were likely responsible for the abundance of spore Cs in the air. It was inferred that the influence of the fungal spores on the atmospheric Cs would last longer since un-decontaminated forests still exist in DRZ.
Yuan, X.*; Hu, Q.*; Lin, X.*; Zhao, C.*; Wang, Q.*; Tachi, Yukio; Fukatsu, Yuta; Hamamoto, Shoichiro*; Siitari-Kauppi, M.*; Li, X.*
Journal of Hydrology, 618, p.129172_1 - 129172_15, 2023/03
Times Cited Count:0 Percentile:0(Engineering, Civil)Wang, Q.*; Hu, Q.*; Zhao, C.*; Yang, X.*; Zhang, T.*; Ilavsky, J.*; Kuzmenko, I.*; Ma, B.*; Tachi, Yukio
International Journal of Coal Geology, 261, p.104093_1 - 104093_15, 2022/09
Times Cited Count:5 Percentile:66.48(Energy & Fuels)Hirooka, Shun; Yokoyama, Keisuke; Kato, Masato
Proceedings of International Conference on Fast Reactors and Related Fuel Cycles; Sustainable Clean Energy for the Future (FR22) (Internet), 8 Pages, 2022/04
Property studies on Am/Np-bearing MOX were carried out and how the properties influences on the irradiation behaviors was discussed. Both Am and Np inclusions increase the oxygen potential of MOX. Inter-diffusion coefficients obtained by using diffusion couple technique indicate that the inter-diffusion coefficient is larger in the order of U-Am, U-Pu and U-Np. Also, the inter-diffusion coefficients were evaluated to be larger at the O/M = 2 than those of O/M 2 by several orders. The increase of oxygen potential with Am/Np leads to higher vapor pressure of UO and the acceleration of the pore migration along temperature gradient during irradiation. The redistributions of actinide elements were also considered with the relationship of the pore migration and diffusion in solid state. Thus, the obtained inter-diffusion coefficients directly influence on the redistribution rate. The obtained properties were modelled and can be installed in a fuel irradiation simulation code.
Endo, Takashi*; Tachi, Yukio; Ishidera, Takamitsu; Terashima, Motoki
Nihon Genshiryoku Gakkai Wabun Rombunshi, 20(1), p.9 - 22, 2021/03
Evaluation method of colloid diffusion and filtration in compacted bentonites was developed using dendrimers. Diffusion and filtration behavior of PAMAM dendrimers with the size of 5.77.2nm was investigated by the through-diffusion experiment in bentonite compacted to 0.8 Mg/m and saturated with 0.0050.5mol/L NaCl. Effective diffusivities (De) and filtration ratios (Rf) of dendrimers were determined from the breakthrough curves and the depth profiles in compacted bentonite, respectively. The De values of negatively charged dendrimer increased when porewater salinity increased and dendrimer size decreased as influenced by anion exclusion effect in negatively charged clay surfaces. The Rf values increased when porewater salinity decreased and dendrimer size increased, demonstrating significant fractions of dendrimer were filtered by narrow pores in complex pore networks. These trends consistent with the previous studies emphasize the validity of the evaluation method using dendrimer.
Yotsuji, Kenji; Tachi, Yukio; Okubo, Takahiro*
CMS Workshop Lectures, Vol.21, p.251 - 257, 2016/06
We have developed integrated sorption and diffusion model (ISD model) for assessment of diffusion parameters consistent with sorption processes in compacted bentonite. The ISD model gives consistent consideration to porewater chemistry, sorption and diffusion processes in compacted bentonite. The diffusion component based on the electric double layer theory and the homogeneous pore model in the ISD model accounts consistently for cation De overestimation and anion exclusion in narrow pores. The current ISD model can quantitatively account for diffusion of monovalent cations and anions, however, the model predictions disagree with diffusion data for multivalent cation and complex species. To improve the applicability of the model, it is necessary to consider the atomic level interactions between solute, solvent or clay mineral, and try that we apply the current ISD model to heterogeneous pore structure. In this study we try the application of the current ISD model to multiple pore structure. As results of numerical analysis of these models, the salinity dependence of effective diffusivity for the multi-pore model is comparatively smaller than that for the homogeneous pore model and the current diffusion model is improved.
Okubo, Takahiro*; Ibaraki, Moe*; Tachi, Yukio; Iwadate, Yasuhiko*
Applied Clay Science, 123, p.148 - 155, 2016/04
Times Cited Count:31 Percentile:73.98(Chemistry, Physical)The pore distribution of water-saturated compacted clay (Na-montmorillonite at 0.8 and 1.4 g/cm saturated by three salt concentrations) was evaluated using H NMR relaxometry and freezing point depression. The populations of interlayer water with four hydrated state and non-interlayer water were calculated from the assumed thresholds. The sample with lower density exhibits higher population of non-interlayer water up to 55%. Low-temperature H NMR experiments in view of freezing point depression indicated that mesopore water in approximately 4 nm space observed in the calorimetric study was considered as non-interlayer water and the threshold temperature. The result showed that population of non-interlayer water by expected from freezing point depression agreed with H NMR relaxometry within 10%. Correlation experiments between longitudinal () and transverse relation times () at -10C suggested that high-mobility bulk-like water molecules existed at a clay density of 1.4 g/cm.
Takeyama, Akinori; Idesaki, Akira; Sugimoto, Masaki; Yoshikawa, Masahito
Journal of Asian Ceramic Societies (Internet), 3(4), p.402 - 406, 2015/12
Shahat, A.*; Awual, M. R.; Khaleque, M. A.*; Alam, M. Z.*; Naushad, M.*; Chowdhury, A. M. S*
Chemical Engineering Journal, 273, p.286 - 295, 2015/08
Times Cited Count:297 Percentile:99.53(Engineering, Environmental)Tanifuji, Takaaki*; Yamaki, Daiju; Jitsukawa, Shiro
Fusion Engineering and Design, 81(1-7), p.595 - 600, 2006/02
Times Cited Count:3 Percentile:24.08(Nuclear Science & Technology)The tritium release behavior from LiO sintered pellets is observed by isothemal heating tests. (1) For 81%TD,The rate determining process is controlled by Kohlrauch strecthed exponential form. Tritium trapped in irradiation defects released with recovering the defects by isothermal heating. (2) For 88%TD, tritium release behavior is controlled by Avrami law (exponent n=0.5). The rate determining process is the connected micro-pore migration process.
Fujii, Kimio
JAERI-Tech 2005-048, 108 Pages, 2005/09
The graphite-moderated power reactor was shut down in 1998 and its decommissioning program is being planned. Various graphites are used in the core of magnox-type reactors and HTTR as core-support structural materials and moderating materials of fast neutrons. For the nuclear graphite disposal, it is necessary to determine especially the treatment of long-lived nuclides, such as C which are generated in the graphite components during reactor operation. As a research, which solves the problem of the C concentration, the cooperative research is concluded between JAERI and Japan Nuclear Power Corp. in 1999, and the research for the basic data acquisition has been advanced up to the present. To find the optimum conditions for C reduction, basic data on oxidation reaction and the structure of graphite materials are indispensable. In the present experiment, we measure the air oxidation characteristics in the temperature range 450800C in Quality1 graphite and IG-110 graphite. Changes in pore diameter and pore size distribution due to air oxidation are discussed.
Takeda, Masayasu
Hamon, 14(4), p.249 - 255, 2004/10
no abstracts in English
Shibata, Taiju; Ishihara, Masahiro
Proceedings of International Conference on Advanced Technology in Experimental Mechanics 2003 (ATEM '03) (CD-ROM), 5 Pages, 2003/09
no abstracts in English
Nagao, Seiya; Yanase, Nobuyuki; Yamamoto, Masayoshi*; Kofuji, H.*; Sorin, Yoshiki*; Amano, Hikaru
Journal of Radioanalytical and Nuclear Chemistry, 252(2), p.225 - 232, 2002/05
Times Cited Count:9 Percentile:51.38(Chemistry, Analytical)no abstracts in English
Yamaguchi, Tetsuji; Nakayama, Shinichi
JAERI-Conf 2002-004, p.325 - 332, 2002/03
When long-lived radionuclides are transported by groundwater through fractures in the rock mass surrounding a radioactive waste repository, their diffusion into pores in the rock matrix and ensuing sorption onto mineral surfaces are expected to retard their transport along the pathways. We have characterized the pore structure of the Japanese Inada biotite granite and confirmed that Fick's diffusion law can be applied to the transport of aqueous species in granite. Effective diffusivity was determined by the through-diffusion method for cationic, anionic and actinide complex species to explore the mechanism of diffusion of the aqueous species. The results of this study enable us to provide a scientifically sound basis for radionuclide diffusion in granite for performance assessment of geological disposal. Future studies should emphasize understanding the diffusion mechanisms in low-permeability engineered barrier materials, data acquisition on long-term degradation of the materials and quantifying uncertainties associated with long-term mass transport analysis.
Ishihara, Masahiro; Takahashi, Tsuneo*; Hanawa, Satoshi
Transactions of 16th International Conference on Structural Mechanics in Reactor Technology (SMiRT-16) (CD-ROM), 8 Pages, 2001/08
no abstracts in English
Ishihara, Masahiro; Shibata, Taiju; Takahashi, Tsuneo*; Baba, Shinichi; Hoshiya, Taiji
Proceedings of OECD/NEA 2nd Information Exchange Meeting on Basic Studies in the Field of High-temperature Engineering, p.225 - 241, 2001/00
no abstracts in English
Ishihara, Masahiro; Shibata, Taiju
Dai-4-Kai Kozobutsu No Anzensei, Shinraisei Ni Kansuru Kokunai Shimpojiumu Koen Rombunshu, p.101 - 108, 2000/00
no abstracts in English
Fujii, Kimio
JAERI-Research 99-050, 99 Pages, 1999/08
no abstracts in English
*; Hieda, Kotaro*; Usami, Noriko*; Yokoya, Akinari; Kobayashi, Katsumi*
Radiat. Res., 131(1), p.72 - 80, 1992/07
Times Cited Count:16 Percentile:57.87(Biology)no abstracts in English