Soil dust and bioaerosols as potential sources for resuspended Cs occurring near the Fukushima Dai-ichi Nuclear Power Plant

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

https://doi.org/10.1016/j.jenvrad.2023.107198

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.

Micro- to nano-scale areal heterogeneity in pore structure and mineral compositions of a sub-decimeter-sized Eagle Ford Shale

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

https://doi.org/10.1016/j.coal.2022.104093

Development of evaluation method for diffusion and filtration behavior of colloid in compacted bentonites using dendrimers

Endo, Takashi*; Tachi, Yukio; Ishidera, Takamitsu; Terashima, Motoki

Nihon Genshiryoku Gakkai Wabun Rombunshi, 20(1), p.9 - 22, 2021/03

https://doi.org/10.3327/taesj.J20.001

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.

Pore distribution of water-saturated compacted clay using NMR relaxometry and freezing temperature depression; Effects of density and salt concentration

Okubo, Takahiro*; Ibaraki, Moe*; Tachi, Yukio; Iwadate, Yasuhiko*

Applied Clay Science, 123, p.148 - 155, 2016/04

https://doi.org/10.1016/j.clay.2016.01.014

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.

Large-pore diameter nano-adsorbent and its application for rapid lead(II) detection and removal from aqueous media

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

https://doi.org/10.1016/j.cej.2015.03.073

Separation of C from irradiated graphite materials, 1; Oxidation behaviors and the changes in pore structure of Q1 and IG-110 graphite due to the air reaction (Joint research)

Fujii, Kimio

JAERI-Tech 2005-048, 108 Pages, 2005/09

JAERI-Tech-2005-048.pdf:25.05MB

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.

Mechanical property evaluation method for graphite materials by ultrasonic wave propagation in porous body

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

Present status of the study on radionuclide diffusion in barrier materials

Yamaguchi, Tetsuji; Nakayama, Shinichi

JAERI-Conf 2002-004, p.325 - 332, 2002/03

https://jopss.jaea.go.jp/pdfdata/JAERI-Conf-2002-004.pdf

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.

Understanding of mechanical properties of graphite on the basis of mesoscopic microstructure (Review)

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

Oxidation behavior of nuclear graphite and the improvement of corrosion resistance and thermal shock resistance of graphite materials by compositionally graded SiC coating

Fujii, Kimio

JAERI-Research 99-050, 99 Pages, 1999/08

JAERI-Research-99-050.pdf:5.37MB

no abstracts in English