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Liu, J.; Dotsuta, Yuma; Kitagaki, Toru; Aoyagi, Noboru; Mei, H.; Takano, Masahide; Kozai, Naofumi
Journal of Nuclear Science and Technology, 60(8), p.1002 - 1012, 2023/08
Times Cited Count：1 Percentile：16.48(Nuclear Science & Technology)
/Fe(0) by bacteriaLiu, J.; Dotsuta, Yuma; Kitagaki, Toru; Takano, Masahide; Onuki, Toshihiko; Kozai, Naofumi
Proceedings of International Topical Workshop on Fukushima Decommissioning Research (FDR2022) (Internet), 2 Pages, 2022/10
Nuclear fuel debris, consisting primarily of nuclear fuel and structural material, was formed during the Fukushima Daiichi NPP accident and exists in the cooling water accumulated in the primary containment vessels. Microorganisms living in groundwater may come into contact with the fuel debris and react with it. To assess the degradation of fuel debris, it is necessary to evaluate the interactions between microorganisms and fuel debris. Here we performed an experimental study on bacterial degradation. A mixed powder of UO and Fe(0) was used as a fuel debris simulant. Bacillus subtilis, which is widespread bacteria in nature and thought to be present at the accident site, was used. The mixed powder was exposed to the Bacillus subtilis in a liquid medium for some days. It was found that the oxidative dissolution of the U(IV) and Fe(0) was accelerated by B. subtilis. A fraction of the dissolved U(VI) was precipitated together with iron precipitates which are probably amorphous Fe(III) hydroxides. The study indicates that microorganisms would cause the degradation of fuel debris.
Liu, J.; Dotsuta, Yuma; Sumita, Takehiro; Kitagaki, Toru; Onuki, Toshihiko; Kozai, Naofumi
Journal of Radioanalytical and Nuclear Chemistry, 331(6), p.2785 - 2794, 2022/06
Times Cited Count：4 Percentile：45.16(Chemistry, Analytical)Remnant nuclear fuel debris in the damaged nuclear reactors at the Fukushima Daiichi Nuclear Power Plant (FDNPP) has contacted the groundwater containing microorganisms for over ten years. Herein, we report the possibility of bacterial alteration of fuel debris. We investigated the physical and chemical changes of fuel debris simulants (FDS) in the powder and pellet forms via exposure to two ubiquitous bacteria, Pseudomonas fluorescens and Bacillus subtilis. In the experiments using FDS composed of the powders of Fe(0), solid solution of CeO and ZrO, and SiO, Ce, Zr, and Si were hardly dissolved, while Fe was dissolved, a fraction of the dissolved Fe was present in the liquid phase as Fe(II) and Fe(III), and the rest was precipitated as the nano-sized particles of iron (hydr)oxides. In the experiment using P. fluorescens and FDS pellet pieces prepared by melting the Fe(0) particles and solid solution of CeO and ZrO, the bacteria selectively gathered on the Fe(0) particle surface and made corrosion pits. These results suggest that bacteria in groundwater corrode the iron in fuel debris at FDNPP, change fuel debris into porous one, releasing the nano-sized iron (hydr)oxide particles into the water.
Liu, J.; Dotsuta, Yuma; Kitagaki, Toru; Kozai, Naofumi; Yamaji, Keiko*; Onuki, Toshihiko
Proceedings of International Topical Workshop on Fukushima Decommissioning Research (FDR 2019) (Internet), 2 Pages, 2019/05
To decommission the Fukushima Daiichi Nuclear Power Plant (FDNPP), it is necessary to estimate the current status of fuel debris and predicate the possible change under various condition. Some microorganisms may enter the plant due to the seawater injection after accident and future defueling activity. In this study, microbial influence on fuel debris under aerobic condition was experimentally investigated. By culturing some bacteria in the presence of simulant fuel debris in liquid medium, the microbial degradation of fuel debris was observed.
Yu, Q.; Onuki, Toshihiko; Tanaka, Kazuya; Kozai, Naofumi; Yamasaki, Shinya*; Sakamoto, Fuminori; Tani, Yukinori*
Geochimica et Cosmochimica Acta, 174, p.1 - 12, 2016/02
Times Cited Count：19 Percentile：53.81(Geochemistry & Geophysics)Although microorganisms possess high sorption capability for lanthanides (Lns), their biological response affecting Lns migration is unclear. We investigated the effects of microbial activity on transformation of Lns by contact of Lns with Aeremonium strictum under metabolically active condition with Mn(II). A biomolecule that specifically complex to Ce(IV) was found to be released from the fungal cell, facilitating the desorption of Ce(IV) from Mn oxide. This biomolecule was not associated with any other trivalent Lns or Fe, which differed from those non-nuclide-specific organic substances released from resting cells, as reported previously.
sp. ME121, isolated from soil as a mixed single colony with 
sp. 32KFujinami, Shun*; Takeda, Kiyoko*; Onodera, Takefumi*; Sato, Katsuya; Shimizu, Tetsu*; Wakabayashi, Yu*; Narumi, Issey*; Nakamura, Akira*; Ito, Masahiro*
Genome Announcements (Internet), 3(5), p.e01005-15_1 - e01005-15_2, 2015/09
Liu, J.; Dotsuta, Yuma; Kitagaki, Toru; Kozai, Naofumi; Onuki, Toshihiko
no journal, ,
In Fukushima Daiichi accident, molten core flowed down the structural materials and formed the fuel debris, which consists of uranium dioxide fuel, iron, zirconium, and concrete. Now the decommission of damaged nuclear plant and countermeasure of fuel debris are under discussion. It is essential to understand the current status of fuel debris and possible change during the defueling activities. Considering the appearance of microorganisms in TMI-2 and Chernobyl plant, the existence of microorganisms in Fukushima Daiichi Nuclear Power Plant was expected. Here, the microbial effect on fuel debris, specially the microbial degradation, was experimentally studied. It was found that oxidization and dissolution of iron and zirconium into the medium would mainly cause the degradation of fuel debris.
Liu, J.; Dotsuta, Yuma; Kitagaki, Toru; Kozai, Naofumi; Onuki, Toshihiko
no journal, ,
After severe accident, some microorganisms have been found coexisting with damaged fuel debris in nuclear power plant. It is accepted that the microbial reaction might affect fuel debris, such as deterioration and dissolution into water. By batch culture of widespread microorganism with simulant fuel debris, it was found that these bacteria would promote the disintegration of fuel debris in this study.
Liu, J.; Dotsuta, Yuma; Kitagaki, Toru; Kozai, Naofumi; Yamaji, Keiko*; Onuki, Toshihiko
no journal, ,
Fuel debris was formed in severe accident in nuclear power plant. After the confirmation of microorganisms in water in damaged plant, it is necessary to consider the element migration of fuel debris. Here, some widespread bacteria were applied. By cultivation with simulant fuel debris, the migration mechanism was estimated.
Battulga, B.; Nakayama, Masataka; Atarashi-Andoh, Mariko; Koarashi, Jun
no journal, ,
A growing attention has been addressed on microbial attachment and biofilm formation on plastic debris especially on microplastics (MPs; sizes: 
5 mm) in the aquatic environment. The current study is focused on bacterial and fungal community composition, diversity, and structure in MP-associated biofilms to emphasize potential alteration of elemental cycling by the presence of MPs in the coastal aquatic environment. We collected MP, surface water, bottom sediment, and coastal sand samples from two contrasting coastal areas of Japan on a seasonal basis. Surface morphology and attached microorganisms on MPs were visually inspected by scanning electron microscopy (SEM). A high-throughput sequencing using Illumina MiSeq was performed in the collected samples to investigate the microbial community composition and diversity among different samples.
