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.

Development of safety design technologies for sodium-cooled fast reactor coupled to thermal energy storage system with sodium-molten salt heat exchanger

Yamano, Hidemasa; Kurisaka, Kenichi; Takano, Kazuya; Kikuchi, Shin; Kondo, Toshiki; Umeda, Ryota; Shirakura, Shota*; Hayashi, Masaaki*

Proceedings of 8th International Conference on New Energy and Future Energy Systems (NEFES 2023) (Internet), p.27 - 34, 2023/00

https://doi.org/10.3233/ATDE231072

This project studies investigation on safety design guideline and risk assessment technology for sodium-cooled fast reactor with the molten-salt heat storage system, development of evaluation method for heat transferring performance between sodium and molten-salt and improvement of the performance, and evaluation of chemical reaction characteristic between sodium and molten-salt and improvement of its safety. The project overview is presented in this report.

Remobilisation of radiocaesium from bottom sediments to water column in reservoirs in Fukushima, Japan

Funaki, Hironori; Tsuji, Hideki*; Nakanishi, Takahiro; Yoshimura, Kazuya; Sakuma, Kazuyuki; Hayashi, Seiji*

Science of the Total Environment, 812, p.152534_1 - 152534_10, 2022/03

https://doi.org/10.1016/j.scitotenv.2021.152534

Reservoir sediments generally act as a sink for radionuclides derived from nuclear accidents, but under anaerobic conditions, several radionuclides remobilise in bioavailable form from sediment to water columns, which may contribute to a long-term contamination in aquatic products. This study systematically investigated the Cs activities between sediment and pore water, which is a direct evidence of the remobilisation of bioavailable Cs from sediments, in two highly contaminated reservoirs affected by the Fukushima Dai-ichi Nuclear Power Plant accident. Our results strongly indicate a competitive ion exchange process between Cs and NH via a highly selective interaction with the frayed edges sites of phyllosilicate minerals to be the major reason for the variability of the Kd values between sediment and pore water, even in the Fukushima case.

Antimony from brake dust to the combined sewer collection system via road effluent under rainy conditions

Ozaki, Hirokazu*; Yoshimura, Kazuya; Asaoka, Yoshihiro*; Hayashi, Seiji*

Environmental Monitoring and Assessment, 193(6), p.369_1 - 369_9, 2021/06

https://doi.org/10.1007/s10661-021-09152-5

Chemical-pressure-induced point defects enable low thermal conductivity for MgSn and MgSi single crystals

Saito, Wataru*; Hayashi, Kei*; Huang, Z.*; Sugimoto, Kazuya*; Oyama, Kenji*; Happo, Naohisa*; Harada, Masahide; Oikawa, Kenichi; Inamura, Yasuhiro; Hayashi, Koichi*; et al.

ACS Applied Energy Materials (Internet), 4(5), p.5123 - 5131, 2021/05

https://doi.org/10.1021/acsaem.1c00670

Applicability of for modelling dissolved Cs concentrations in Fukushima river water; Case study of the upstream Ota River

Sakuma, Kazuyuki; Tsuji, Hideki*; Hayashi, Seiji*; Funaki, Hironori; Malins, A.; Yoshimura, Kazuya; Kurikami, Hiroshi; Kitamura, Akihiro; Iijima, Kazuki; Hosomi, Masaaki*

Journal of Environmental Radioactivity, 184-185, p.53 - 62, 2018/04

https://doi.org/10.1016/j.jenvrad.2018.01.001

A study is presented on the applicability of the distribution coefficient () absorption/desorption model to simulate dissolved Cs concentrations in Fukushima river water. The simulation results were in good agreement with the observations on water and suspended sediment fluxes, and on particulate bound Cs concentrations under both ambient and high flow conditions. By contrast the measured concentrations of dissolved Cs in the river water were much harder to reproduce with the simulations. By tuning the values for large particles, it was possible to reproduce the mean dissolved Cs concentrations during base flow periods (observation: 0.32 Bq/L, simulation: 0.36 Bq/L). However neither the seasonal variability in the base flow dissolved Cs concentrations (0.14-0.53 Bq/L), nor the peaks in concentration that occurred during storms (0.18-0.88 Bq/L, mean: 0.55 Bq/L), could be reproduced with realistic simulation parameters.

Application of measurement and evaluation method on the clearance system of the Fugen NPP for dismantled equipment of turbine system

Hayashi, Hirokazu; Soejima, Goro; Mizui, Hiroyuki; Sano, Kazuya

Proceedings of 23rd International Conference on Nuclear Engineering (ICONE-23) (DVD-ROM), 7 Pages, 2015/05

In the Fugen Nuclear Power Plant, we are going to conduct appropriate classification of the waste according to the contamination level of the material of the plant, to reduce the amount of radioactive waste and to promote dismantling work rationally and efficiently. For this reason, we are going to apply the clearance system to the dismantled material generated from dismantling work of the turbine system, and to reduce the radioactive waste amount as much as possible. In order to operate the clearance system properly, the target nuclides need to be selected accurately, and the evaluation method of them should be established. The assessment was conducted as follows.

Research on consequence analysis method for probabilistic safety assessment of nuclear fuel facilities, 2; Basic experimental data aerosol release fraction and trial analysis in boiling event of radioactive solution

Yoshida, Kazuo; Hayashi, Kazuya*

Nihon Genshiryoku Gakkai Wabun Rombunshi, 9(1), p.60 - 70, 2010/03

https://doi.org/10.3327/taesj.J09.003

A special committee of "Research on the analysis methods for accident consequence of nuclear fuel cycle facilities (NFCF)" was organized by the Atomic Energy Society of Japan under the entrustment of Japan Atomic Energy Agency for a research on the state-of-the-art of consequence analysis method for Probabilistic Safety Assessment (PSA) of NFCF such as fuel reprocessing and fuel fabrication facilities. The objectives of this research is to obtain the basic useful information related for establishing the quantitative performance requirement and for risk-informed regulation through qualifying issues needed to be resolved. The research activities were mainly focused on accidents with more severe consequence than design basis such as events of criticality, explosion, fire and boiling of radioactive solution. The research results are summarized in this technical report about basic experimental data related to key phenomena postulated in boiling event of radioactive solution.

New synthesis method of advanced lithium titanate with LiTiO additives for ITER-TBM

Hoshino, Tsuyoshi; Kato, Kenichi*; Natori, Yuri*; Nakamura, Mutsumi*; Sasaki, Kazuya*; Hayashi, Kimio; Terai, Takayuki*; Tatenuma, Katsuyoshi*

Fusion Engineering and Design, 84(2-6), p.956 - 959, 2009/06

https://doi.org/10.1016/j.fusengdes.2008.12.049

LiTiO is one of the most promising candidates among the proposed solid breeder materials for fusion reactors. Addition of H to inert sweep gas has been proposed for enhancing the release of bred tritium from breeder material. However, the mass of LiTiO was found to decrease with time in the hydrogen atmosphere. This mass change indicates that the oxygen content of the sample decreased, suggesting the change from Ti to Ti. In order to control the mass change at the time of high temperature use, the development of lithium titanate which has LiTiO additive is expected to be effective.

Concentration profiles of tritium penetrated into concrete

Takata, Hiroki*; Furuichi, Kazuya*; Nishikawa, Masabumi*; Fukada, Satoshi*; Katayama, Kazunari*; Takeishi, Toshiharu*; Kobayashi, Kazuhiro; Hayashi, Takumi; Namba, Haruyuki*

Fusion Science and Technology, 54(1), p.223 - 226, 2008/07

https://doi.org/10.13182/FST08-A1800

Concentration profiles of tritium penetrated into cement paste, mortar and concrete were measured by using samples with a shape of column. Tritium penetrated until a location of about 5 cm from the exposed surface after 6 months' exposure. The amount of tritium penetrated into mortar and concrete were less than 70% and half that into cement paste.